Help with my Radeon Hd 7870

Hey guys I'm struggling here, I just built a whole new computer and I'm having trouble even playing Crysis 2?? I'm playing on an 46in LCD 1080p TV. my drivers are updated and I'm getting 20-24fps in the game and it doesn't even change when I lower the graphics or resolution?! I run Diablo 3 with maxed out everything at 85-90fps and it looks great! It did install a big update for windows 8 when It finished installing the Crysis 2 maybe this has something to do with it? Thx guys any help would be greatly appreciated.

My build

i5 3570k 3.4ghz
XFX Radeon HD 7870
G.skillz Ripjaws X 8GB Ram
Corsair CX750
Seagate 1TB HD