MY 9800Gx2 DONT WORK ANY MORE HELP PLEASE!

hello all i have major problem i hawe asus 9800gx2 and i play call of duty 2 in windows 7 with dx9 with 333fps constant and dx7 600 fps constant all work great , but i reinistal windows 7 and i get fps 150-max 200 but not constant in call of duty 2 i get 280 fps in dx7 and not constant i got newest drivers all inistaled i tray xp 64 , vista ultimate 64x nothing any one hawe any idea please help me ? or my grapchis card die when i turn on 16x AA in crysis warhead he youst turn it off and game lagg

Here are my spec:

Manufacturer: ASUSTeK Computer INC.
Processor: Intel® Core™2 Quad Processor Q9300 ~ 2.5GHz
Memory: 8192MB RAM
Hard Drive: 250 GB Total
Video Card: NVIDIA GeForce 9800 GX2
Monitor: LG W2252S
Sound Card: SoundMAX HD Audio
Speakers/Headphones: Yes
Keyboard: Logitech Media Keyboard 600
Mouse: Razer Lachesis - Phantom White
Mouse Surface: Razer Goliathus Control Edition
Operating System: Windows 7 Ultimate 64-bit
Motherboard: ASUS P5NT-Deluxe
Computer Case: LC PRO 906S

*** ing ways i using win xp 64 bit now cus i wannt to fix this problem or i go to asus service