Computer a little slow lately

theres a number of things you can do... get a nice virus detecter such as ad-aware se personal... which is free ware...and run a full system scan... delete all files that it finds... also you can go to your start menu and click on search... type in cookies... and delete those... then type in temp* and delete those... or if you running IE 7 then just go to tools>history> delete all... update your virus definitions... defragment your harddrive... uninstall unnecesary programs... uprgrade your memory... hope that helps..
Before you start. I seriously recommend backing up all your documents. Things like the ‘My Documents’ folder, game saves and other program configurations. Nothing should go wrong; but, it does please be prepared; as I shall not be held accountable. You can also utilise Microsoft Windows System Restore – always a good idea to do this before you make a major change to your computer.

Basic Solutions
Simple Stuff
Keep these things in mind when using your computer.

* Don't open E-Mail attachments from people you don't know, and if you do - be careful, run a virus scan on them before opening.
* Don't run files you don't trust, especially if they are just bare .exe files from a dodgy source.
* Once you've downloaded a file, run a virus scan on it. Just to make sure, it can't harm you.
* If your antivirus tells you you've got a virus in your temporary internet files, stop browsing that page immediately. Close all internet pages, clear the temporary internet files and run a full system scan.
* Before running a virus scan, clear your temp internet files and clean out the Sun Java Temp folder.
* Pay close attention to the task manager, if you see a new process there, and you haven't installed anything - be cautious, it may be legitimate - but do some checking anyway. Google the process name, and run a virus/adware scan.

Windows XP Service Pack 2
If you’re using Windows XP, and don’t have Service Pack 2 installed – install it!
Microsoft’s Top 10 reasons to install Service Pack 2.
You can get it here. Once you’ve downloaded it, Microsoft and I recommend:

* Check here for programs that might behave differently when using Service Pack 2.
* Check here for programs that may stop working when using Service Pack 2.
* Backup all essential data, My Documents, game save files, program configurations etc...
* Do a full system scan for viruses, using all the anti malicious software programs you have. This is covered in more depth below.
* Check for special update instructions from your computers manufacturer.
* Once you’ve made backups, scanned for threats, and installed. Instantly check for Windows Updates (see below).

Windows Update
Although this will not speed your PC up, it will keep it safe, run Windows Update regularly. (Only works in Internet Explorer)

Office Update
Although this will not speed your PC up, it will keep it safe, run Office Update regularly. (Only works in Internet Explorer)

Update Everything Else
I can't tell you where to go to update your programs. But I can tell you. Look through every program you have, and download every available update for it. The programs you have may contain fixes in the program, or security related issues.
AutoPatcher seems to be a good program for generally updating all installed software (that’s supported, and you have). Everytime I reinstall Windows, or get a little behind on installing program updates, I use Autopatcher all the time.

Very simple solution, defragment your Hard Drive. This simply rearranges the files in your hard drive into a logical order, meaning your computer will spend less time looking for the files. A simple diagram can be found here.
To do this, follow the instructions shown in this picture, then highlight the selected drive, and click "Defragment".
For a better Disk Defragmenter, see Perfect Disk 7 below.

Disk Cleanup
This simple program included with Windows deletes ( / compresses)
some unused/unnecessary system files, such as:

* Downloaded Program Files
* Temporary Internet Files
* Offline Web Pages
* Office Set Up Files (If you have it)
* Recycle Bin
* Temporary Files
* WebClient/Publisher Temporary Files
* Compress old files
* Catalog files for the Content Indexer

To use this, follow the steps in this picture. Select the drive, if you have more than one (or of you have several partitions). Then select the options to cleanup, and then press "OK". For more info on getting rid of junk on your computer, check CCleaner below.

Add/Remove Unused Programs
If you installed a program to try it, and didn't like it. UNINSTALL it, why keep it lying around in your Hard Drive? Or if a program doesn't work, uninstall it. Or if you just plain don't use it for any reason, uninstall it.

Start-Up Appliations
If you've just bought a new computer, or have just installed a whole series of applications chances are you'll have a few programs which start with your computer; many of them unnecessary.
For a start, if you know there's an application stating with your computer and you don't want it to: open up the program and look for a way to stop it starting. This method is advised, as using MSConfig can just lead to the program re-adding itself.
MSConfig isn't immediatly accesable to any user, you've got to do this to use it: Start>Run>msconfig>Startup
As shown in these pictures:
Untick the things you don't want to start when your system does, although if possible disable the application starting in the program.

Disable Un-needed Services - Only for more advanced users
I've decided, I was going to make a guide about disabling unneeded services, but I have now decided that it is too big a topic for me to do. So here is the best guide I can find on how to do so.
Black Viper's Guide to Disabling Services Black Vipers site is currently down, although there appear to be some mirrors of the original guide, just Google 'Black Viper Service'.

Third Party Solutions
Mozilla Firefox
Controversialy a better internet browser than Microsoft's Internet Explorer. It is a radical departure from IE6, although Micrsoft is closing the gap between Firefox and Internet Explorer with IE7.
Has many extra features; the main ones to be noted are:
Search Bar, Tabbed Internet Browsing, the use of extensions and greater customisability.
Mozilla's Homepage.
Download here.
Once you’ve installed Firefox, you’ll need some plug-ins to make some sites work properly. You can view the essential plug-ins here.
NEVER Uninstall Internet Explorer, you need it for running Windows Update.

Perfect Disk 7
This program makes you wonder why you even used the Microsoft Disk Defragmenter.
Among other things, it defrags your HDD(s), and optimizes the files, defrags your system page file, and the master file table. Altogether these things may seem insignificant, but together, they've sped up my PC immensely. The computer now boots in about 4 passings of the loading bar. Perfect Disk 7 is made by Raxco Software
Download the trial here.
I really urge you all to buy this software, it's by far the best disk defragmenter that I've tried.

CCleaner vaguely resembles the built-in 'Disk Cleanup' in Windows, although it removes far more and support for cleaning of new applications is being added in almost every revision.
Great program to remove unneeded files from your computer. It deleted 700MB (the first time I ran it), and 1.5GB from a friend’s. Also has a basic registry cleaner. Great all round cleaning program. CCleaner Homepage.
Download here.

I'm taking recommendations for new free Registry Cleaners, RegCleaner is a few years old now.
This great program searches your registry for un-needed registry entries and deletes them. (It also makes a back up, before you start). Download here.
Once installed you need to allow it to clean the registry automatically; to do this select "Options" > "Registry Cleanup"> "Method" then select "Automatic". To then clean the registry select the "Tools" option > "Registry Cleanup" and then "Do them All".
This program is no longer supported.

Cerulean Studio's Trillian
This IM client integrates MSN, ICQ, AIM, YIM and IRC. So you don't have to have 5 programs open at once eating up your ram. Cerulean Studios’ Homepage.
Download here.

AIM Ad Hack
If you use AIM, you might want to consider using AIM Ad Hack instead, it removes all the rubbish from AIM (including the other applications it installs; which you probably don't want). I use this, although I do not use AIM a lot it makes the program a whole lot more bareable.
AIM Ad Hack Homepage.
Download here.

A-Patch for MSN/WL Messenger
Quick and easy program to remove all the rubbish from MSNM/ WLM. If you're fed up of nudges, packs, adverts, tabs this is the perfect application for you.
A-Patch Homepage.
Download here.

Virus/Trojan/Adware/Spyware Problem & Firewalls
Everything above can slow down your computer, although open doors in your security protection can caused havoc. So, make sure you have a firewall, and antivirus which are kept upto date.
Microsoft® Malicious Software Removal Tool
Simple tool for removing malicious thingies, just download and run - no installation required. The web version checks for really common malicious stuff.
Scaled Down Web Version
Full Downloadable Version

Windows Defender Beta 3
Revision of the Seems excellent, and if you keep it running in the background it queries most suspicious activities. Up to you whether you keep it running in the background, but definitely download, install and run a scan every so often.
Download here.
Microsoft have a guide on how to install and configure the program here.

Ad-Aware Second Edition
A great, free Spy/Ad ware solution. Detects and deletes most Spy/Ad ware.
Free definition updates. Second Edition. Made by Lavasoft.
Download here.

Spy Sweeper
A great, free Spy/Ad ware solution. Detects and deletes most Spy/Adware.
You need to pay to get definition updates. Made by Webroot Software.
Download here.

Spybot - Search & Destroy
A great, free Spy/Ad ware solution. Detects and deletes most Spy/Ad ware.
Free definition updates. It finds the same as Ad-Aware, if not more. Made by Safer Networking.
Download here.

NOTE: I use all four of the above. So that if one program misses something, the other three are bound to pick it up (I use Spyware Blaster too). I recommend you use them all to, just to make sure nothing gets missed.

Spyware Blaster
This great program stops spyware and adware before it even hits. It protects you against malicious ActiveX programs, cookies and much more. Read here for more info. Made by Javacool Software.
Download here.

Think you’ve got the well known Trojan/spyware CoolWebSearch on your computer?
Well you can use this handy tool to get rid of it.
Download it here.

HijackThis - Only for more advanced users
Serious spyware infestation? Especially with Internet Explorer, this will help get rid of those pesky search bars that just keep coming back. This programs requires a slightly higher level of computer literacy.
Download it here.
Confused by HijackThis' results? Post them here for a detailed analysis.

Online Virus Scanners
These online virus scanners can be useful to check if you have a virus, which your antivirus has missed.

* Trend Micro Nice online scan, can be used with almost any internet browser.
* Symantec Security Check Good, but you need to use Internet Explorer
* Jotti's Malware Scan Great scan, utilises many virus scanners to check if the file. Almost bound to find the virus. Can only check on file at a time, but this is very useful.

This free anti-virus program by AntiVir is one of the best free AV programs out there. According to this thread at AndandTech AntiVir has the highest virus detection rate among free scanners.
Download here.

avast! 4 Home Edition
Anti-virus program by alwil software is one of the most used free antivirus options. (The one I use)
Download here.

Firewall Check
Want to check how effective your firewall is to external elements?

* GRC Shields UP! Great all-round scan, checks all commonly used ports and more.
* Symantec Security Check Nice scan by Symantec, sad they try to sell you stuff at the end – even if you pass perfectly.

Sygate Personal Firewall
This free firewall by Sygate is generally revered as one of the best free firewall around. (The one I use)
Download here.

Zone Alarm
This free firewall is made by Zone Labs. It’s your decision whether you use Sygate Personal Firewall or this, both are very good free firewalls.
Download here.

For more PC security advice, check this excellent post by qUiCkSiLvEr

RAM - Random Access Memory
Your computer needs this stuff, and the more the better. Any 32bit CPU (Intel Pentium 3, 4, Celeron. AMD Athlon XP, Barton, Sempron) can take 4096MB or 4GB of RAM. A 64bit CPU (AMD Athlon 64, Opteron. Intel Pentium 4 with EMT64, Xeon with EMT 64, Itanium) can handle hundreds of GB of RAM, but the amount a certain system can take is limited by the motherboard and chipset.
One simple solution to speed your PC up, is to buy more RAM for it. Just check what speed of RAM your Motherboard and CPU can take, and what the maximum amount of RAM your computer will make use of.

Solution = Buy more RAM
The cheapest places to buy RAM, that I know are: - USA Only
eBuyer - USA (Maybe Canada) and the UK (maybe mainland Europe)
Overclock - UK & Ireland

Hope all this helps. And if you have any other solutions, tell me, and I'll add them to the post. But I think I've covered most of it. One last thing is, there are only so many things you can do. There is no good replacement for good computer hardware.