Yesterday my computer just turned itself off, without warning as if someone had unplugged the power from the computer, and then when I tried to turn it back on from the power on botton on the tower it wouldn't turn on. I looked inside the tower and I could see the motherboard light was not lit, I then turned the tower off from the on/off switch at the back and turned it back on, after several times of doing this the motherboard light lit up and I then was able to turn the computer on again.

It worked fine but later it did this again.

So today I have been searching for answers, I looked on the help section here, I don't THINK any parts are overheaing, I downloaded speedfan to check the temp of my machine and everything seemed normal. I then thought to try a stress test, I used OCCT and after 30secs into the test the computer just turned off again.

I checked everything in device manager and that LOOKS fine.

After doing some searching, I read somewhere than someone else had this problem and they fixed it by turning the PSU the right way up, my PSU is installed the wrong way up (I think) so I tried to flip it round but then the screws and the holes wouldn't match so I had to LEAVE it upside down. This is a custom built machine that I built myself and its been working fine for nearly a year.

Any help would be much appreciated, thanks.I would swap in another power supply of = or > wattage......The stress test could indicate under load the PSU is failing...did you have any other recent power issues leading up to the failures?...You can check the power cord from the PC to the wall as well to be certain it's well seated.Thanks for your response, the power cord seems fine, and i havent had any recent issues leading up. I haven't got anothe rpsu to test it with but maybe i can locate one later.

Whilst running the stress test on the cpu, i also had the speedfan programme open which was monitoring temperatures, this time when the stress test was runnig it aborted saying cpu got too hot, it then showed me a bunch of graphs showing the time and the cpu temperatures rising as time goes along. The temperatures were reaching nearly a 100, so what can I do, i have got the fan onto of the cpu which is running okay I think.I'll assume it's clean inside.....have you moved the PC recently before the problem started?...Make sure all the fans are running, make sure the clips holding the fan on the cpu is secure and the heatsink is flush to the processor/MB. When you run speedfan , check the voltages for anything that seems out of the ordinary.....good point Karnac I recently installed some RAM so I will have a look inside the case, clean it up and make sure everything is tight, what do you mean check the voltages, what should they be?

Thank you Karnac for your help so far.Just be sure the + voltage numbers are close to the voltages listed.....if you have dislodged the heatsink or a clip wasn't secure , you'll need to reapply thermal paste....reseat all cards, ram, check all connections are snug.,,,,,,Practice ESD (static) safety as wellThe voltage numbers were close to the numbers listed, I think I did dislodge the heatsink so i have secured that for now and then when I can get some thermal paste I will apply that and see what happnes then.
Thanks once again for your help

Edit: Any explanations as to why when the computer turns off it takes so much effort to get it back on, the motherboard light goes out and then I have to keep turning the tower switch on and off to try to get the motrherboard to light up again. Sometime when I turn the tower on the motheroard lights up BRIEFLY before turning off and then I have to keep FLICKING the switch until finally the light stays lit.
Is this some sort of safety feature?
Thermal Paste GuideQuite possibly.......PC power supplies provide a power good signal to the MB which prevents operation when abnormal supply voltages are present.........still might be the supply causing problems.