Tonight my desktop computer shut itself off. (I'm using
the laptop now). I started it again a few minutes later
but it shut down again after only a few minutes. I assume
it's overheating, but I verified that the fan is running.
I realize this may be tricky to diagnose, sight unseen,
but does anyone have any idea about what may be happening,
and is this something I might be able to fix myself?

Thanks in advance.