PC works fine, then won't work, then works just fine again

[Webster_1]

This is the weirdest problem I ever had and I dont even know which category to put it in.
I'm a computer technician which means that yes I have checked the cables and if the psu is ok, I have already fixed hundreds of computers and I honestly have never seen anything like that.

Here is the deal: In the office I work at, there is 3 computers, one of them is the one I use to do web related work. At one day I was working using this computer just fine, I finished my work, turned everything off, closed my office and went home.

the day after I went there to use this same computer again, but it just would not turn on no matter what, I tried replacing almost every component and it just would not turn on, so I was like "well I've got other stuff to do so I'll deal with this tomorrow"..

the day after I went to fix this computer with more patience and guess what? it turned on normally and showed no problem whatsoever and worked just fine the whole day, I tried turning it off just to see if it would turn back on and it did normally, I tried replacing components again to see if I accidentally putted one that was working (and not working yesterday) and it was fine too, no matter what I did it wouldnt show any problem whatsoever.. So I was like "well I guess now I've seen everything, just happy it is working." and here we go again...

the day after, I went to work in that computer again, and it again, would not turn on no matter what, and there's been two weeks now, (I normally have other stuff to do so I just go to another computer and deal with it later) for two weeks it turns on normally in one day and wont turn on in the other, once it worked for three days straight with no problem and then went back to not want to turn on.

Here are commom problems that the pc doesnt have (in the days it is working)
-it does NOT freeze, does not stutter, does not overheat, none of that.
-it does not shut off by it self (never did) even during heavy rendering work it wont turn off.
to resume: in the days it is working it does not present ANY kinda of problem WHATSOEVER.

So far I have 3 conclusions:

1-The motherboard is tired and old so it only works one it wants to.
2-That pc is trolling me just for the lols.
3- Some demon is possessing it.


I even checked in the security cameras to see if someone was getting in my office to mess with me but nope. Hope anyone has any better conclusion than the 3 ones I've got so far.

Thanks

 

[CBender]

Maybe it is a power issue in your office. Have you tried to plug it somewhere else? Generally power related issues exist because of a faulty power supply. It could be that the psu doesn't get all the juice and love it needs under certain conditions and decides to throw a tantrum.

 

[Leaps-from-Shadows]

Or maybe there's a switch somewhere in the office that controls the plugin that computer is getting power from. Somebody turns the switch off, the computer won't power on. They leave the switch on, the computer works normally.