Problem with counter strike source

Hi just installed counter strike source today it's not the first time i wanted to test the game on my new AMD Radeon HD 6870 graphic card but when i try to open the game it goes on the loading screen and then close i tried restarting steam and reinstalling my graphic card drivers but still doesnt work someone help please?

Sorry for my bad english.

Make sure EVERYTHING is updated.

I looked into the problem but everytime I find something similar it's because of NVidia related graphics cards. Try going onto a friends computer, going onto your steam account, and installing/playing the game from there. I know it's a computer problem but it could be a rare chance that something is wrong with your account.