Cannot launch Halflife 2 or garry's mod

[wumbo6]

I just installed a 6800 graphics card on my computer and when i try to load halflife 2 through steam it says preparing to launch... then the window dissapears and nothing happens. also with battlefield 2 i launch it and it gives me a black screen. when i check task manager there is a program battlefield 2 and error. i cannot bring the error message to the front but when i end one they both close. can anyone help me? thanks

 

[The General]

did you reinstall the drivers?

 

[wumbo6]

i did this started happening when i installed lost coast.