Computer Starts up but shuts off immediately, repeats until PSU is switched off.

[Duploboy]

So my parent's computer started doing this and they're usual repair guy was booked up. So i opened up the case and saw right away that as it tried to start up all the fans were spinning except the CPU fan. I knew that the MOBO might be shutting it down since it wasn't reading anything from the CPU fan, as a safety feature. So i replaced the cooler and the problem persists. At least now though the CPU fan is spinning.
So now I'm assuming that the CPU must have burnt out because the fan wasn't working. Is that a correct assumption? If it wasn't for the fact that the CPU fan wasn't working I would assume that the PSU was the problem but as best I can tell it seems to be working. (I did the paper clip test)
I'm prepared to replace the CPU but I don't want to get a new one just to discover that it was actually the PSU all the time.

 

[DRagor]

CPU is not going to burn out that easily. You would have a lot of forewarning like pc shutting down often if the temp was the problem. As long as heat sink is properly attached to CPU it can safely operate at least few minutes even without fan. I've even had CPU operate without heat sink for few minutes and it's still good to this day.

Said that, PSU is on top of the list, but actually it could be anything failing, mobo, cpu ,ram, gpu even drives. Best to check hardware one by one.

 

[Duploboy]

CPU is not going to burn out that easily. You would have a lot of forewarning like pc shutting down often if the temp was the problem. As long as heat sink is properly attached to CPU it can safely operate at least few minutes even without fan. I've even had CPU operate without heat sink for few minutes and it's still good to this day.

Said that, PSU is on top of the list, but actually it could be anything failing, mobo, cpu ,ram, gpu even drives. Best to check hardware one by one.

Hmm i recall my dad saying he was having issues with it shutting off randomly. So you recommend starting by replacing the PSU and going from there?

 

[DRagor]

If it was shooting off randomly then it is very likely the CPU was the cause. Since you did the paperclip test, the PSU might be good. So the next step should be disconnecting all drives, removing GPU and memory, and trying to boot the comp. If you get beepcode meaning 'no-ram' (assuming you have beeper installed on the motherboard), that would mean CPU, PSU and motherboard are ok. If you get silence, then considering the fact that fans spin, it's most likely CPU.

 

[NerdIT]

In addition to what DRagor said, I would also try resetting the CMOS/BIOS by removing the C2032 battery (flat, quarter sized watch battery on the motherboard) and putting it back in.

EDIT: Remove all the drives and stuff, but leave one stick of RAM in - the board may not post without any memory.