The village where I live was sat under a thunder cloud for most of Friday, and we suffered a few power fluctuations (specifically, what seemed to be split-second outages). When I got back home from work, I found that my PCs had shut down during one of these outages. When I went to boot one of them back up, I couldn't get anything to display on screen, nor did the boot seem to complete correctly. I tried a number of things - unplugging different bits of hardware, swapping graphics adaptors, etc. - to no avail. I thought I was looking at a fried motherboard or CPU. Power seemed to be distributed correctly to the peripherals (the drives all appeared to be working) so I figured it couldn't be the PSU. Eventually I unplugged it from the mains and left it overnight (approx 12hrs unplugged). I tried it again this morning, and it booted up correctly. Woo-hoo!

I have all my equipment protected by surge-protected power strips, so I don't think a spike caused these problems. Obviously it has something to do with the power fluctuations, and maybe the PSU in the problem machine got itself confused somehow.

The questions are, for future reference and to help people with similar problems:

1. What are the likely causes of the boot failure I experienced?
2. Is a UPS a simple and cost-effective solution, or might other things help prevent this happening in future?
3. What UPS can you recommend (my budget is limited)?