Help! cant play l4ld2

[SmackCrocaine]

ive had l4d2 for a while now and have been playing it with no problems, (exept for the game crashing a few times but thats cause i went a bit overboard with mods) i havent played it in the last month because the game will not start, i mean, itll do the valve screen and the intro movie, but when the l4d2 loading screen comes up a lillte blue circlle by my mouse appears and then it closes the damn game! if anyone knows whats wrong please help, i would apreciate it so much, plus im not very computer gaming litterate so i dont know what most thing are called. oh and i have windows eight -_-

[NekoButts]

Have you uninstalled the mods?
You can always try this, right click on L4D2 in your library, click properties, local files and in that menu click "verify integrity of game cache" which essentially reinstalls the game for you :)

[SmackCrocaine]

wow thank you very much! really appreciate the help :) the steam community really is a beautifull thing :D thank you again :D