Try and turn off, "Numlock" and see if that changes it.
On keyboards that so not have a Number Pad it can change some letter keys to numbers when Numlock is turned one.
This may have something to do with that.
I don't have a clue if it has nothing to do with numlock.
You could try running the game in Windows view so that you can minimize it and check to see if the game changes the Numlock setting when is starts.
On laptops this can be solved by hitting the FN key or the FN key with the Numlock key but since it only does it in the game the game has to be changing something.
i figured out what was wrong with modern warfare. when i tried to start mw2 up it told me "Do you want to optimize your setting to fit your computer?" i selected no and it works perfectly. I still dont understand what's wrong with left4dead...