Grumble wrote:

I've been pulling my hair for 3 hours over this problem, so I thought
I'd ask in here, and see if people have had a similar problem.

Thanks Keith, CJT, George, and Tony! Your insight was very helpful.

The problem was the PSU indeed. In my (rather limited) experience,
PSU-funkiness is quite hard to diagnose, as there are many very
different possible symptoms. I'm thankful the PSU didn't take out my
other components when it died (which happened to a friend).

In the end, I payed only 14.50 EUR for a no-name 400W ATX PSU.

--
Regards, Grumble