Consider my entire neighborhood lucky? I've got half a dozen friends, all gamer's, all in houses of the same general age with ungrounded outlets. Between us you are talking about a combined 100+ years of computer ownership. There's no shortage of houses all over the country with two prong outlets. I see no evidence of widespread issues caused by ungrounded outlets. In fact the other AT thread was the first result when I Googled "ungrounded computer".
Most of the lengthy threads on other forums on the subject point back to the same thread on Tom's Hardware which like all the other threads don't have any actual evidence of ungrounded outlets causing widespread computer failures. Once again, I'm not saying it
can't cause problems, but the suggestion that I'm "lucky" for NOT having issues has no basis in reality. That implies I'm the exception rather than the general rule.
If 1 user in 10,000 has an issue because of a non-grounded outlet, that doesn't make the other 9,999 the lucky ones. That makes the one user the unlucky one. People have been using computers on ungrounded outlets for 30 years. I've got a friend who's got 15 systems of the P4/A64 era that all run at once for lan parties on ungrounded outlets and have been doing so for many years. Yeah, the lights flicker when the AC comes on. Yet the computers keep running fine. We've tripped the circuit breaker on more than one occasion, yet the computers come right back up.
It would be different if we were talking about me having one computer that didn't have a premature failure. But between myself and half a dozen close friends we are talking about probably 75 computers that have never had a premature failure. A 75-0 record either indicates I should be buying more lottery tickets or the power issue isn't as big as people are making it.
I think people are severely underestimating a computers ability to deal with power fluctuations. But more importantly there's a simple way to test the power fluctuation theory. Just about every BIOS on the planet shows you voltage readings. If it's having issues while web browsing, that indicates it's not dependent on a high load. Therefore he should be able to see fluctuations in the BIOS to see abnormal smaller spikes and it should lock up or reboot at some point.
I could argue the UPS stabilizing your system indicates you have a crappy power supply/motherboard that doesn't handle power spikes. Or that (based on the thread in your sig) that you are running a power supply too close to capacity which would make the system more sensitive to power fluctuations.
Is that the case? Maybe, maybe not. But one instance of a UPS improving system stability is no more conclusive then one case of not having issues with ungrounded power. You say you are trying to save his system, that's great, but at what cost? I don't know about where he lives, but here to get the house completely rewired to modern standards would be like $10k. Is it possible the electricity is the issue? Yes. But I'm certainly going to do far more testing before plopping down that kind of cash on a hunch.