Computer shutting down randomly - NOT overheating

Question

Desktop PC running windows 7, hasn't been formatted in about 3 years.

I recently installed & run skyrim for about 1 week with no problems (up to that point I hadn't run any recent graphics-heavy games). Then, the pc started shutting down on its own (no hangs-no blue screens) while playing. I lowered the graphics settings and it seemed to go better.

About a week after that, yesterday, the PC started shutting down on its own WITHOUT running Skyrim or any other graphics-heavy applications.

I checked the system temperatures and CPU temp was very high. I opened the case and there was a lot of dust, so I cleaned it carefully. Afterwards, CPU temperature was way lower (about 55 C).

However, after that, the computer STILL shuts down, now very very frequently (after about 3 mins after boot). It always happens in windows, although I don't have any other OS installed to test. I did try to leave it on BIOS for about 15 mins, during which time it did NOT shut down, but that might have been pure chance.

I have been checking all temperatures when booting up, and none of them are high just before the computer shuts down. No other changes have been made to the hardware/software recently, only running Skyrim, that's why I mentioned it. Once again, these new shut-downs have nothing to do with the game and happen randomly and frequently.

Also, sometimes, after these irregular shut-downs, pressing the button to switch on the pc doesn't work properly (it sounds like it's trying to switch on but fails).

Any idea on what can be wrong?

edit : Temperatures seem to be fine now, windows are genuine, there's no visible damage to motherboard or other hardware.

According to comments, I'll try booting a Linux live CD (Good idea!) and a different PSU for now, thanks.

edit2 : Changing the PSU seems to be working. System has been running for a few hours now with no shut downs.

edit3: I can now confirm that the culprit was a semi-functional PSU. Case closed

Solution

Changing the PSU to an identical one (same wattage) worked, seems like it was half dead but pretending to be alive.

Comments

[and31415]

It looks like a hardware issue. What happens if you boot some Linux live distribution?

[Jet]

Is your Windows activated? I've seen random shutdowns on computers which were running not genuine Windows 7.

[evan.bovie]

What's your hardware specs? Could be a mobo issue.

[Ƭᴇcʜιᴇ007]

Probably hardware, try a new PSU. While you're in there, examine innards for damage and/or out of place components, clean out dust, etc.

[tomconte]

How exactly did you “cleaned it carefully”? Could you have nudged the heatsink off the CPU?

[Jalal Mostafa]

It might be caused by a RAM overheat , check if they are getting too hot

[SJG]

Remove your RAM and clean contacts with eraser. Make sure you clean the whole system with high pressure DRY air or electric blower! Hold any fans down with your finger while blowing it out. Also make sure your heatsing did not move. If it did move and the thermal paste got "broken" and you can not replace it immediately, you can wipe it off completely and have a dry contact between the CPU and heatsink. Check all connections and check for those small dust clogs that appear on the board

[spuder]

@surfmadpig, If you found the solution, will you create an answer for it and accept it?