I have had this same problem on two separate computers I have built and I am still trying to resolve it.
Here are the specs for my first computer:
OS: Windows Vista Home Premium
CPU: E6600 Core 2 Duo 2.4Ghz
HS: Thermalright Ultra -120
PS: Corsair 620HX
HD: 2 36GB RAID 0 Raptors via PCI card
MB: GA-965P-DS3 REV 3.3
MEM: Corsair 2x1GB DDR2 800 XMS2 later Crucial Tracer 2x1GB DDR2 1066
VID: 256MB XFX 7600GT
DVD: 2x Samsung SH-S183L
CASE: Antec Nine-Hundred
When I installed Vista Home Premium on the first computer it would restart about 30 minutes into the install every time. Finally, after a few days I got Vista to completely install, after many issues with my RAID setup, only to have the system restart on me every time I tried to boot.
Initially I thought it was a memory problem , so I bought 2x1GB Crucial Tracer DDR2 8500 because it was supposedly guaranteed to be compatible according to Crucial, its speed would match up with my processor's FSB, and the lights would let me know if the memory was actually functioning or if it was an issue elsewhere.
I got the memory and installed it, still the reboots persisted. After this I spent more time doing research and less time spending money on parts that wouldn't fix the problem. I kept restarting the system until I got the voltage for the memory set correctly as well as the timings. Finally, after hours of restarts it worked again.
The only problem came later when I installed Fedora on the same RAIDed hard drives as Vista and my Grub installer would no longer recognize Windows Vista, but thats not a problem for this thread.
Here are the specs for my second computer:
OS: Windows XP Pro 64-bit
CPU: Pentium D 930
HS: Intel Standard Heatsink
PS: Thermaltake 400W
HD: 250GB WD 2500KS
MB: GA-965P-DS3 REV 3.3
MEM: Corsair 2x1GB DDR2 800 XMS2
VID: 256MB XFX 8600GT
DVD: My old Lite-On DVD drive
CASE: Antec Nine-Hundred
My second computer started out much easier than the first in that I was able to use the old memory (Corsair) that had not worked in my previous build to install the OS (Windows XP). However, once I got the OS installed and was running the system for a few days it started to do the constant restarts as well.
I tried moving my new Crucial memory from the other computer over and it didn't work at first, not even turning on, but later it was the only thing that would work after some tinkering in BIOS.
Finally I had one working computer, or at least I did up until 3 days ago when the second computer decided to do random restarts on me as well. I am at such a loss I don't know where to begin. In a last ditch effort I decided to buy some Kingston DDR2 800 1.8v memory hoping that will run.
I even promised my wife that if it doesn't work I will give up on these computers and the hundreds I have spent trying to get them to work and buy her a DELL. I really don't want to start all over again with a new computer so if anyone has any advice now would be a great time.