reset your bio's to defaults and try again. Memory timing or your fsb could be rebooting you. Not sure how your bio's are setup tho so its hard to say. Go defaults on everything and check all your internal connections IE. power cables and ide/sata cables. Its usually the most simple things that cause problems lol.
Intel Q9550 ( 3.84ghz OC on air)
Asus Rampage Formula
OCZ Platinum dual channel memory 8gig
Vista Ultimate 64bit
Radeon 4870 512mb