Gmod and now l4d2!

Could anyone help me? i set my Gmod to -dxlevel 80 and it loads but goes to a black screen and now my L4D2 wont load. after the cutscenes it closes out and says hl2.exe has stopped working im hoping someone can help oh and also my L4D2 is set to -dxlevel 80

L4D2 doesn’t work in DX8 mode.

Your graphics card sucks.

get a new gfx card

Acquire, for yourself, a new card that provides graphics.