Fact: The roof in our house has NO insulation in the roof.... At all. Typical 50s house.
Fact: Heat rises.
Fact: Our computer room is upstairs.
Fact: My CPU was reported running at 65°C.
Unknown: GPU temps.
I was working on my homework, combined with the above.
Sudden "click" from PSU.
Blackscreen. No fans.
*heartsink*
Wait a couple minutes, I'm able to get into BIOS.*phew* there.
Couple problems gone
The thing I'm most frustrated with is that there was no overheating warnings.
Duh, just realized: I have no system speaker!
Leaving it off overnight.