Please help me

hi there my system is

mobo asus p5q3 deluxe
ram asus ddr3 1333 2x1 giga (comes with the mobo)
gpu asus gtx 275
sound card sound blaster x-fi
cpu intel core quad q9650
hard drive 400 giga(dont know what brand)
lg dvd
psu corsair hx520w


I am running windows xp32 bit and my system is fresh formated
I am getting blue screens of death when i am just in windows
and when i am playing games or in games it just get me out at desktop
generaly the system is unstable. I put my old asus 8800 gtx and all is great
i know that the the problem is with the gtx275 but i dont know what.
can anybody help me. I forgot to mention that the blue screens its not always the same i believe that is my psu but i am not sure and i dont want to spend money for nothing please help

thanks

thanks for the request my friend
but i have tried all the drivers i found old and new

something else?