You might've already did it, but have you verified your Steam cache for TF2 yet?

Verfied files again, redownloaded, etc. Still doesn't work. I've just sent a support ticket to steam, hopefully I'll get a response soon. This is extremely frustrating..
You trying to use any plugins or do you have additional .dll's in your TF2 folder? Sometimes foreign .dll's can cause launch and crash errors. Valve is always screwing over some addon to the game with every patch.
did you reinstall and all that annoying stuff?....i have personally been fighting valbve to get Left 4 dead 2 to work they updated it and it hasn't worked since