After nearly 6 years, it seems the power supply in my computer has decided to go flaky.
The problem started about a week ago when the computer abruptly shut down on me. After a few seconds it powered back up, and didn't happen again for a while. Then the sudden shutdowns started to become more frequent. Sometimes the computer would stay running overnight, other times it would shut down 3 or 4 times in rapid succession. It would stay running for a few hours, then boom. Other times it would be up for a few minutes, then boom. Frequent but intermittent.
Primary suspect was the power supply. I reseated all the cables going from the power supply to the motherboard and wiped the BIOS, but that didn't help things. Then I noticed the main power switch on the power supply was broken and didn't toggle on/off anymore. Seems like a good candidate to cause such problems.
While the power supply was the main suspect, I wasn't able to rule out other problems too like something bad on the motherboard. Fortunately someone in the Charleston Tech Slack (if you're looking for geeky tech-y people to connect with, sign up here) had a couple of 650W power supplies he was willing to let me borrow. They're smaller than the 800W supply currently in the computer, but 650W is enough to run things.
Disconnected the old power supply from everything and connected the loaner. Since the power supply is just a loaner, I didn't bother with putting it in the case.
Computer's been up and running on the loaner power supply for a few hours now with no issues so far. Compared to what the computer had been doing before, that's a significant improvement and a good sign that something in the power supply is faulty. I'll keep it going for a couple more days to see how things go, and if everything's ok I'll order a new power supply to replace the original one.