I suppose I've been fairly lucky. Hardware doesn't tend to explode dramatically for me; the only things I've really lost are removable storage media, and even then that's nothing compared to a friend of mine, who mainly has taught me to never buy PC Line (PC World's own brand) blank media: their data integrity didn't even last long enough for him to copy files from one system to another. Silver foil flaked off, the works.
I was, however, forced to do a system rebuild some time ago, which I thought had been tracked down to the motherboard (replacing the PSU didn't do anything in this instance.) New board, new RAM, new PSU. It's started happening again, and partly because the troubleshooting could take a long time and involve buying parts, and partly because the system is sufficiently old (RAM, socket A, IDE) that getting them is increasingly a case — when buying new, and troubleshooting with second-hand parts is a potential nightmare — of paying close to the price of contemporary components whilst not getting the benefit or performance of them, I've just bought a Dell business system. It's due in a week or two.
I'm moderately sure the problem is the PSU. The trouble with PSU problems is a) they can potentially damage other hardware, which I suspect is what happened to my last motherboard, and b) the readings available through software can appear stable, but a multi-meter attached to the supply is the only way to know for sure. Since I don't own one and have what I consider to be a healthy fear of electricity, I can guess and replace the PSU and maybe other things or make a choice to upgrade entirely.
Judging by the 1.6 VCore, the Duron I've got is a Spitfire version, first introduced in 2000. The RAM is more recent, with the hard drive probably being more of a bottleneck. At 40Gb, it's working space rather than storage.
The troubleshooting process...
There isn't anything registering in Event Viewer, a piece of software built into NT-based operating systems that logs service and driver problems. This suggests Windows didn't see the problem coming, and that it's more likely to be hardware at fault. The USB wireless stick and external drive plugged into the system both power down when things hang. Video output is maintained, so the monitor can be unplugged and reconnected and still have the same stuck image — which made me think that RAM might be the issue. I haven't overnighted Memtest86 or Memtest86+ for a longer test, but a drawback of software testing is that they wouldn't be able to access the shared graphics RAM. I've no old and reliable AGP cards lying around, and no real reason to suspect the memory in there (Crucial brand, IIRC) is at fault.
USB power isn't lost; if an LED 'snake' light is plugged in it doesn't go out — it's just the connections with the stick and drive. All fans are whirring away, and optical drives still open. What else? I've recently cleaned a lot of dust out of the PSU, though its fans were operating fine. The capacitors on the mobo all seem level. The system had been off for a couple of months whilst I was away, and I dimly recall one or two system freezes earlier in the year that didn't recur after fans were cleaned and more downtime than usual allowed for. The system has no extra cards, two optical drives and one internal hard drive, so it shouldn't be drawing undue power. There's a case fan in there and a fan cradle attached to the hard drive.
A slight sudden voltage dip, particularly on the 12V rail, would easily explain the freezes; it wouldn't even be noticed by mechanical components, but the RAM and processor require more reliable power feed.
It's been a good system. It's roughly my second (since in the course of upgrades I built an entirely separate box from parts, it's a real stretch to claim otherwise: the floppy drive is the only original component... and that was itself the only non-new component when the first box was built.) Paired with Windows 2000, it takes a shot at anything asked of it — it runs jEdit so that the interface is responsive enough to be usable, as a rough benchmark. Video encoding is the only thing that's really a strain. Compared to most other systems, though, it isn't responsive and anything current offers a major upgrade.
I haven't gone for an entirely baseline system. Dell's barest bones box is a Celeron / 512Mb / 160Gb / DVD-RW for 165 including delivery (okay, you could shave fractionally more off with just a CD-RW, I suppose...) For 90 more, you double the hard drive and memory and get a dual core processor. And naturally, this won't be running Vista, which is another factor in the decision to start over: XP systems are thinner on the ground these days, as Microsoft try to railroad business customers towards a new OS with many proven teething problems. Dell, like other big system-builders, is fighting to continue offering XP because professionals fail to see the point in spending more on hardware for little perceived extra benefit and a slew of OS support issues. XP flies on hardware that Vista considers a bare minimum; it's perfectly usable on the ~800MHz/256Mb Thinkpad I'm typing on.
One step behind is a good policy with Microsoft operating systems, though I can't see Vista ever being as warmly regarded as NT5/5.1 — by now, XP is a known entity, coming of age with SP2, with workarounds for annoyances such as activation and administrator passwords long in place.
Most of all though, I'm just hoping this system will be quieter, have a reasonable PSU and run stably.