It's very hard to troubleshoot a PC "virtually". You should know full well a CMOS reset is the first port of call. His overclock is drawing more power from the PSU for a start and it's increasing the temps. It's good practice to troubleshoot from stock settings.
I've already said the PSU is a candidate for the problem (post #11), trouble is his temps are quite high.
2500K intel spec sheet
the Tcase is 72.6 degrees (that's not the max safe temp just the highest the Tcase sensor should ever read) so you are looking 80 degrees before heat is causing issues.......he is showing temps close to that. If he tried realtemp and a few other programs he'll see that the recorded temps can vary from program to program.
I'll make some assumptions and go out on a limb and guess the PSU is faulty. Infact maybe even the fan has failed in the unit. At 50 degree temps it will struggle to maintain it's output. Seeing as it's an old PSU it's not going to putting out was it was new anyway.
If the fan was sucking warm air in from the case it would run warmer but at the same time was helping to cool the CPU. The hotter your components are the shorter they live is the rule of thumb.
If the machine is still failing at stock speeds. Investigate the PSU, easiest way is to use a known working PSU. Can you borrow one from a friend (a good 500W PSU is all you need for that system)?
I would bet that will solve your problem, If you have had the PSU 3 years thats good going to be fair but I am suspecting you need to look at your case cooling too. What case and fans do you have installed and where is the computer kept?