It is differently a hardware problem on your old rig.
Either weak power supply, faulty CPU or bad motherboard. But without replacement parts to swap out to find out which one it is then you may never know for sure.
Honestly, if you tried a different power supply and the problem still happened I would say it is the motherboard for sure. The reason why I say that is I have seen plenty of times where a power supply is going bad and isnt giving out enough power and so hardware doesnt work like it should and things crash or lock up. I have also seen parts of a motherboard go bad. I had a laptop a few years back that blue screened on anything you tired. I tested memory and hard drive and couldnt find what was doing it.
I then got a hold of a hardware tester software that tested everything and I mean everything, things like DMA access on the motherboard and all kinds of different sections. While running that test EVERYTHING came out fine, then it got to the DMA test and sure enough it failed every time. DMA is on the motherboard and is used for direct memory access. And so I found the problem, it was the motherboard. But I would have never of known why the board was bad without that tester.
I still use a older version of the program after all these years, it is expensive to get the new one lol
QuickTech Pro PC Diagnostic Tools
http://www.uxd.com/qtpro.shtmlShane