I sent the motherboard off to MSI for repair/replacement - coz there was a known fault (random power offs, just like I was getting) with that particular board in that particular serial number range. But when they tested it they said there was no fault. Tho they didn't tell me that till I asked for a status report after a coupla weeks. So, they sent it back. And it arrived back with the heatsink broken off.
Which wasn't, as you can imagine, good news. Took a wee while (" it's quite impossible for the heatsink to get loose by itself." no shit, sherlock, damaged in transit methinks *rolls eyes*) but eventually they took it back & tested it again & said it was perfectly fine (with the heatsink reattached, obviously, but I'm not convinced it was re-seated well).
Of course that took another week or so of it being away & it didn't actually fix the problem that'd started the whole thing. I tested what I could (again, in some cases) - not PSU, not gfx, not harddrive, not floppy drive, not DVD drive - but eventually I bit the bullet and started flinging money at it. Obviously first port of call was mobo/cpu replacement and we decided I might as well have a proper upgrade so now I have a Gigabyte EP35-DS3R mobo + an Intel Core2Duo E8400 cpu, so my machine goes zoooooooooom! ;)
I think I've pretty much got most of the reinstallation done, tho there's a few bits & bobs left to do in linux to get it precisely the way I'd like. Only a month & a half after it stopped working reliably :/ In some ways shoulda just bought stuff in the first place, but it wasn't my turn for an upgrade (J's machine is older than mine) so we were trying to sort it out on the cheap ...