you need to find your day of defeat icon in steam library. Right click and go to properties.
Click on the update tab and make sure "always keep this game up to date" is selected.
Now click on the local files tab and click on "verify integrity of game cache"
This will take a few minutes and will force your game to update.
If that does not work, you have either a firewall or router blocking steam's ports to the internet most likely.
-Blue