Odd computer behavior, can't pin it down

[Biftheunderstudy]

First here's the hardware:
E6420 at stock speeds (was overclocked but behavior the same at all speeds)
-Xigmatec cooler on it
Gigabyte DS3R revision 1.0 newest bios
2x1Gb Corsair 667
2x512Mb Mushkin 667
300Gb Maxtor as a data drive
160Gb Seagate as the OS drive both SATA
XFX 7800GT
OCZ 600 watt game xtreme
Windows Vista home premium with service pack 1

The computer hard locks and reboots randomly, no blue screen or memory dump. Yes automatic restart is disabled. It seems to do this mostly when it loaded, prime95 can run for hours sometimes and others but a few minutes before it happens and memtest came up with nothing.

Any thoughts?

 

[wanderer27]

I try it with just the 2x1GB or 2x512MB RAM.

My thinking is there may be some type of Memory Timing conflict or maybe Memory slot mismatch. Some MB's are set up so that Memory pairs need to be in certain slots - for mine it's 1 & 3 and 2 & 4 (yeah, I know it's older).

Other than that, just make sure you have all the Chipset Drivers for you MB installed.

 

[robisbell]

I concur, memory may not be compatible between the 2-1GB and the 2-512MB.

 

[Biftheunderstudy]

I pulled the mushkin out, computer still reboots randomly. Sometimes while idling on the desktop, others whiles gaming.
Power supply?

 

[vanvock]

Sounds like this is not a new build but been together & ok for a while, is that the case? Have you looked in event viewer to see if there is any indication of a problem? You might try removing componets one at a time to see if it clears up. Is (was) anything overvolted? Good air flow? What are temps?

 

[Biftheunderstudy]

Been running for almost a year. Nothing in the event viewer since it won't memory dump just hard reboot. CPU was overclocked but well with reasonable temperature/voltage ~50 degrees loaded, 1.45volts.

I've reflashed the BIOS, new drivers for everything, manually set the ram timings to 5-5-5-15. Since doing this I haven't seen the problem crop up again, *crosses fingers*