Issue installing WinXP

Not sure what is going on, maybe someone has some insight...

Have a system that I put together a few years back and just recently it started to shutdown without notice. Seemed like it was overheating, so I installed a newer case fan but that did not help.
A few days later, it shutdown and that was it. Was able to pull the HDD and put in another system of the exact same configuration and the worker is using that just fine.
But on his previous system, I tried several things... replacing the power supply, the processor fan... no good. Tried to put in a new HDD and format it but came up with a "no hard drive located" error.
Ended up getting a new MB, new RAM, new processor/cooling fan and the new HDD. Only thing not new is the case and power supply.
So I have tried a few times to install the WinXP OS (same one that was installed previously) and it goes through the basic setup and once it gets to the point of actually finishing up the Windows install (setting time/installing window programs/etc) it throws up the dreaded blue screen.
I am at a loss... thinking of trying a different power supply unit but it would seem to me that this is more software than hardware... but could be wrong.

I know I haven't listed the specifics of hardware but wondering if anyone has a clue to what is going on?

bgunn