Fremen

I hope you guys can help.
My computer will shut off in the middle of something, or when it's just sitting idle.
It started doing this 3 nights ago and hasn't stayed on for more than 45 minutes at a time, if that long.
Most times the screen goes blank, my Numbers lock button lights up, and my optical mouse goes dead.
I've unplugged the power cords, mouse cord, and various other cords and re-plugged everything, to no avail.
It won't stay on.

I bought the comp. from Dell in 2002 and haven't upgraded any of the hardware.
Every once in a while, before this problem started to happen, I'd hear a high-pitched whine from the tower, which I assumed was the harddrive, from what I've read on here in y'alls posts, but then it would quit and I'd hear no more for a few weeks or months.

About 6 months ago, a buddy that knows a little bit more than I do about computers, cracked mine open and blew out the interior with canned air.
So it should still be relatively clean.

Do y'all have any ideas about what it could be?

Thanks for your help.

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