I just downloaded Call of Duty 4 from steam as I pre-ordererd MW3 and the game will not work.
The single player work, however I can not see it. The screen is frozen on one frame but its making the sounds and moving the mouse you can tell when it goes over the buttons plus when you minimize and go back to it, a more recent frame is shown.
Also the multiplayer says iw3mp.exe has stopped working after showing the splash.
Im running a 6770 with 8Gb ram and a i3 2100 processor, all of which should work fine. I have new games installed such as Dead Island and they work perfectly.
Steam is full of problems, So i would suggest that you just buy the game instead of downloading it form steam.
Or you could try to format and update steam and windows, Sometimes you might have a virus or a worm that destroy some parts of your win32 files without you noticing it, Even when you have an anti virus program there is always viruses out there that can bypass any anti virus program
go to your harddrive and search for the game and search for cod and make sure there is no file left on your drive, Then try reinstalling and keep an eye on the installation to make sure there is no problems and try again,
When you downloaded the game was there a delay or an error?
Try alt+enter while running the game. This 'should' bring the game into windowed mode. That ways, you could have an opportunity to play around with the graphics settings within the game. Lower the resolution, etc to see if the game is working, then alt+enter again to go to full screen.