Okay the rig is as follows:
Athlon X2 4200+ Manchester @ stock (AC Freezer 64 Pro)
DFI Ultra-D Motherboard (passive heatsink on northbridge)
2Gb RAM (1x1Gb Super Talent and 1x1Gb Kingston Value)
X1950Pro standard cooling @ stock
Enermax Noisetaker 600W PSU
1x HDD (Seagate IDE)
1x Rom drive (brand unknown)
The general problem as of about 24 hours ago is that when running a 3D app the PC will crash in the first 2/3 minutes, and struggle to boot immediately after, unless it is turned off for a few minutes to cool before trying to reboot. This problem seems to have first started when I switched from my North-Q 400W PSU to the Enermax. Note, the PC seems fine for the most part when at desktop!
The crashing isn't immediate. First the screen goes to standby, I can tell the PC is still responsive as the sound effects still respond to mouse commands. Around 5 seconds later the PC hard crashes and is unresponsive with the sound looping/frozen.
Before installing the Enermax a few weeks ago, with the North-Q i was getting random blue screens, which I put down to the memory, but after running Memtest for a good 2/3 hours on each stick and having 0 errors it seemed to suggest the memory was fine, hence trying a new PSU.
I have since switched back to the North-Q PSU and I'm getting the crashing as per the Enermax. I intend to do a full system strip and rebuild to see if that sorts the problem, but assuming it doesn't what are the likely causes for this kind of crashing.
I realise the symptoms point to overheating. I'm fairly confident it's not the CPU I have core temp and speed fan running, which suggest at full load the max temp it's reached is about 57C (full load), I'm not sure how to measure the X1950pro but I have VPU recover enabled and "prepare an error report" ricked in the ATI control panel, and a screen hasn't popped up asking me to send one. Thus I can only assume this 1950 is fine too (always was before anyway).
I have tried one stick of RAM with the same crashing, so that suggests the RAM isn't at fault either. The only other option is overheating on the motherboard? Can anyone shed any light onto this, or suggest a course of action / other things to consider.
Many thank guys
PS I also have a spare motherboard (ECS Nforce4-A939) but don't want to do a complete reformat. What do I need to uninstall to switch motherboards?