Hi!

It's more of a heat issue than a power supply problem. Things in there get
too hot, as do the other parts of the computer that are cooled by that fan.
That in turn causes malfunctions.

Have a look inside the power supply, the motherboard and any expansion
cards. Check to see if there are any exploded or bulging capacitors. If
there are any in the power supply, just replace it. If you wait, something
will go "bang!" and that may ruin your computer's hardware. I'd replace the
motherboard and expansion cards as well if they show signs of having been
too hot (exploded or inflated caps again)...but I've seen heat-damaged
boards that kept on running without issue.

William