Help with new computer and windows

Hi im new here can u guys help with my problem.

ok heres my problem, i just switched back to windows xp proffesional from vista ultimate 64bit(cause vista didn't like my computer) and every now and then my computer will freeze right after it logs me in so i pressed the power button for 3-5 seconds to restart it after leaving it sit for 5-10 mins, now it gets to the windows loading screen and then flashes a BSOD and reboots. i didnt always get the BSOD after a reboot sometimes it would boot and freeze again, then on the third reboot it work. but now i get only the BSOD any help would be greatly apperciate.
thanks in advance.

PC Specs:
Motherboard: Gigabyte M57SLI-S4
RAM: 4gigs of A-Data ddr800 (2 x 2gig sticks)
CPU: AMD athlon 6400+ black edition(stock speeds)
Video: MSI 8600GTS(factory overclocked)
HDD: primary: WD 500gig sata secondary: 320gig Seagate satat
PS: Thermaltake Purepower 500w

there are no other cards installed just video