memory - Is my PSU faulty?

My PC has recently started freezing. I've narrowed it down to the following facts (using DDR RAM):

• 2 modules in Single Channel mode, it takes some hours to freeze.


• 1 module in Single Channel mode, it takes some hours to freeze.


• 2 modules in Dual Channel mode, it takes about 2 minutes to freeze.


• 2 modules in Dual Channel mode, with memory speed underclocked, it takes some hours to freeze.

Memtest running for 10+ hours for each module shows no errors. I've also tried with another pair of RAM and the results are the same. Also, about 1 month ago, 1 HD and 1 memory module were broken and had to be replaced.

Are these good indicators of a faulty PSU? It shouldn't be a heating issue as the temperastures are OK and the PC has multiple fans working.

Specs:

• mobo: ASUS P5GD1 Pro


• CPU: Pentium4 3Ghz (Prescott)


• PSU: BeQuiet! 350W


• RAM: Patriot 2x512MB DDR400 (also tried with Corsair 2x1GB)


• OS: Ubuntu

Edit:

Temperature readings: CPU 48ºC, MB 37ºC, graphics card 48ºC. Chipset heatsink passes the "finger test" and fans are OK. Using cpuburn, temperatures raise quite a bit but there's no freeze.

Additional info: in dual channel mode, if I boot into console-only mode, the system doesn't freeze right away, only after some time (say, 30 min.). However, the system freezes immediately the moment I start the desktop environment (GNOME).

Conclusion:

The problem is still present with a different PSU and also after trying different components for everything except for the motherboard and CPU. Between these two, perhaps it's most likely a motherboard problem.

Answer

First of all, 10 hours of memtest does not yet guarantee you'd spot the error. Some errors can take days to be revealed.

However, as you've cross-tested with another set of memories, it sounds like either motherboard or PSU would be faulty. Because memories and their settings affect the freezing frequency, I would first suspect the motherboard, especially since on P4 it's the chipset that controls the memories.

Are you running the latest BIOS available to your motherboard?

Check also chipset temperatures; if the heatsink is too hot to keep finger on it, then it's, well, too hot. Fans die over time, so it's possible the airflow in the case has lowered too much causing the problem. You can check that the fans work properly by putting a wooden pencil between the blades and then checking that it starts rotating right away; if it looks like the fan has trouble starting to spin again, the bearings are dying and it's time to swap the fan.