how can i see if my graphics card can use directx11? because i think it doesnt 
What is the make and model of your graphics card?
nvidia geforce 7900 gs
I believe the 7900 only supports up to direct x 9, shader model 3.0. The 8800 series was the first to support direct x 10 (shader model 4.0, and the first direct x 11 cards were the GT300 series (shader model 3.1 oddly).