Random computer reboot

[rokytnji]

It is probably hardware related. The part that throws me off is it has been fine for a long time.
A computer I dug out of a dumpster and turned into a Linux testing and media center.

Well. It would turn on when I was not there. I figured it was bios related to wake up after a period of time.
If no bulging capacitors or the ram check checks out with the  memtest link.

I'd be afeared the power supply may be the culprit. Since it is intermittent.  I would reseat 20 or 24 motherboard connector (the big one) in case a loose
connection over time is causing this. I will also mention heat causes electrical mechanical contacts to expand. Like a female socket expands when mated
with a male connection pin. My fix is to dig into the connector with a thin blade jewelers screw driver and try and compress the female socket a little tighter.

The green wire and the black wire are the 2 main connector pins I would be concerned with on 20 or 24 connector. They are the main power pins going to your Mobo to power the board.  (Black is ground, Green is power).

I don't envy you as I have a dead mini atx shuttle box under my desk that is not worth fixing anymore iMO.
It has bigger problems than your desktop pc.

Edit: Just to explain myself a little better. The pins I am referring to are dc power. Think of it like the battery cables on your vehicle getting loose and you tapping them to make good contact. My suggestion is non destructive. Requires no parts replacements. Just reseating the plug is all I would do 1st and then see if the reboot pattern resumes. Then work my way further from there with trying to compress the female pin socket to get a better grip if the reseat did not work.