PC shuts down in Windows 7 full mode

Does anyone know what causes my PC to shutdown in Windows 7 full mode after only a few minutes of booting up yet will run in Safe mode indefinitely. I have reset the BIOS to default, run various antivirus procedures, run Malwarebytes etc. but to no avail. The PC is an HP s3240uk which admittedly is old by today's standards but had been very reliable until the last few days when this problem reared its ugly head. Any practical suggestions?

Does it shut down gracefully or not?

Overheating cpu caused by heatsink clogged with debris?

In reply to a post by petsy:

Overheating cpu caused by heatsink clogged with debris?

Indeed, if its the latter answer to my question that would be my first guess.

I had already assumed that the CPU was possibly a factor and cleaned out any dust etc. but to no avail. The PC shuts down without warning yet runs well in Safe Mode.

In reply to a post by petsy:

Overheating cpu caused by heatsink clogged with debris?

Have considered removing CPU and refreshing the thermal paste but didn't want to do this without first checking other options.

More likely to be an errant device driver. Are there any clues in the event log?

In reply to a post by BatBoy:

More likely to be an errant device driver. Are there any clues in the event log?

Will check, but as a point of interest I note the warning 'device driver software was not successfully installed' appears when starting in full mode. This seems to refer to the mass storage device which relates to the built in card reader. I have no idea as to how this could have occurred because it is part of the HP setup which until these recent problems was never an issue!

In reply to a post by Pipexer:

Does it shut down gracefully or not?

It does not shut down completely without me holding the power down button. Another new discovery ... I was running an instructional video in full mode via YouTube when suddenly the PC shut down without warning. However, the odd thing is that the sound continued after the shutdown. What does this indicate ... maybe the passively cooled graphics card is overheating? It runs at around 65 degrees C but I can't recall this being much lower.

If the sound was still going then the PC hadn't shut down. It suggests you have a monitor or graphics card problem as it seems it is the screen going off rather than the PC.