Windows 7: Freeze 5870 HD

Hello everyone,

I just got a new graphic card XFX Radeon 5870 HD @ 2Gb and have somes following problems :

Often i have some freezes, its locked up. No blue screen and no reboot automatically, i have to make a manual reboot. On the orther hand i heard sound freezes. i dont know where it comes from. Drivers of the graphical card are up to date. I upgraded my BIOS. Re install windows seven,done mem test. Nothing change i think i have done all things as possible and nothing change. if someone gots an idea ? Thx for answer
(Excuse my english im french )

Regards,