It was only when I removed the old motherboard that I noticed some of the capacitors around the processor had burst slightly leaving a ‘rusty’ residue on the top of the capacitors so a few weeks later when another PC was having similar problems I took a close look and found the same blown capacitors there. Replacing the motherboard fixed it.

I’ve now had around 10 PCs with the same problem – all of them were around the same age (around 3 – 5 years) but had different motherboards so I suspect a bad batch of capacitors were around at the time of manufacture.

So if you get a PC that just does what it likes when it likes and can’t figure it out shine a torch on the motherboard and particularly the capacitors around the processor – healthy ones should be shiny and silver (unless covered in dust), if there’s any sign of bulging and a brown risidue of leaked electrolyte then consider it unreliable or likely to become unreliable!