I7 xp 32 bit crashing

Hi - I have just built a new i7 920 for a mate, he does graphic work so he needed XP 32 bit OS so as to be compatible with his current software(he will upgrade in the near future).
I used a Gigabyte EX58-UD3R board with 6GB of PC3 12800 OCZ Gold memory, a Zalman 750Watt PSU, CPU is i7 920 with standard cooler, 7200rpm Western Digital Cabiar drive, LG Dual layer +/- burner and Quadro 4850 graphics.
My problem is that the system starts up and seemed to run fine but then simply would reboot. It stays running fine in bios, and I have tried a Windows repair and a full fresh re-image. These haven't worked, the system kept running fine whilst it was loading the OS, then when I loaded all the drivers all was well, but then it crashed and restarts when Windows is simply starting and running for a minute or a few seconds, or before it even fully starts. The OS is Service Pack 3......
Am I missing something important about compatability of the OS here with the i7 ??? pls help - desperate to get this fixed asap!
Karl