Computer Reboots Unexpectedly..

[Brolli*]

First of all Im new and just wanted to say hi.

anyway I got a new mobo for Christmas and cpu and now all of a sudden, without warning my pc reboots on its own while playing a game, no colored screen, no error, it just reboots.
My games start up fine, good fps, and fine ping. I can start up a game and it will play fine for about 5 hours straight since I put in a new PSU but evantually it will reboot.
It doesnt reboot while on my desktop, web or installing games just when im playin em.
I googled around and found that it could be caused by overheating, but my temps are fine. Everything's(mobo, gpu, cpu, harddrive) around 10-50ºC .
I updated video card driver, mobo drivers, auto, etc... I ran MemTest on my RAM individually for 7 passes and it came up with no errors.
I also unchecked the 'Automatically Restart' box from the Computer Properties and it still reboots. Im expecting its my mobo since I tested everything else but there still may be somethin else before I order one...

Here are my Spec:
OS: Windows XP Pro w/SP2
Processor: Intel Pentium D 775 3.4GHz
RAM: Crucial PC2700 1024mb(512x2) DDR
Motherboard: MachSpeed P4MSD-800
GPU: BFG 7800GSOC 256MB AGP
PSU: Ultra 700watt (40amp and 12v)
CPU Fan: Masscool 8W0141B1M3G (w/ masscool thermal compound)
Case Fan: Ultra Blue 120mm Fan Ball Bearing

Anyone have any idea how I can fix this problem? Thanks

 

[Elbatrop1]

Start by reading the guide at the top of this forum:
http://www.techist.com/showthread.php?s=&threadid=61766

If that doesn't set you straight, post back

Also, resize your sig. The max size is 468x120. I could do it myself, but I think you'd prefer if you did it

 

[LA1]

did you put your old install of xp on the new mainboard ?
if so that could be what is wrong
do you get a BSOD ? Does it just flash by ?
if so
click start
click run
type sysdm.cpl
hit enter
click advanced
then understart up recovery
click settings
uncheck auto reboot

when you get the next BSOD, WRITE DOWN THE ERROR CODE, and post it here , we will then help you

 

[Brolli*]

Start by reading the guide at the top of this forum:
http://www.techist.com/showthread.php?s=&threadid=61766

If that doesn't set you straight, post back

Also, resize your sig. The max size is 468x120. I could do it myself, but I think you'd prefer if you did it

I checked my CPU temp in my BIOS and it stays at 35ºC so I dont think my CPU is overheating.

I just got a new PSU, its an Ultra 700watt (40amps on the 12v) so I dont think its my PSU

I checked my RAM using Memtest individually for 7 passes and no errors came up.

I also did a full virus on my pc two times and it came up with nothing. =/


Im getting no BSOD when my PC reboots, my game just freezes for a second, then my screen go black then Im at the memory testing screen where you are able to enter your bios.. Im thinking its my mobo because Ive tried everything..