theres a few questions before i presume anything that id like to know.
1 Does the pc make any noises besides the fans ie a beep or a slight clicking noise.
2 Do you have a hard drive light if so is it flashing or working?
3 As others asked do all fans seem to run including videocard.
4 what motherboard do you have or pc model if its a name brand ( Need this to test more options outside of the first 3 questions.
5 Try unseating and resetting memory hd and videocard. I know you said you checked the chords but make sure these things are firmly seated because all 3 can cause that symptom if not.
6 Do you have a spare video card while its unlikely this given the little info so far are we 100% sure the video card didn't die and that the pc is turning on? *this is extremely unlikely but some older boards wont load if this is the case while extremely unlikely i still make sure its not with out knowing the board model

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Also if your pc your currently using can log into vent i should be on all day may be a bit easier to work with someone directly to troubleshoot if you have time im usually around the opx ps2 rooms.
*also for those asking yes i saw the keyboard mouse part however that does not 100% mean the board yet with out knowing these answers

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