Dear Lazyweb, I need your help. My main desktop has started falling over under heavy load. That’s when playing games and when encoding video or some other computationally intensive task. It switches off, the monitor goes black and all parts stop spinning/whirring, though the power light is still on.

I tried a PSU tester and it shows no fault. I tried memtest86 but it switches off after a short time. I don’t think I have suitable spare RAM to hand and I don’t have a spare motherboard or CPU. I may be able to lay my hands on some but I think they may be borked.

I’m normally excellent at identifying hardware faults but this time I need your suggestions.