Enermax is the opposite of crappy PSUs, but even quality PSUs can go bad.
The first thing I'd check is the RAM.
If the motherboard has onboard video, try removing the GPU.
After that, try a clean install of an OS on the same hard disk (this rules out the HD and the OS). Make a new partition for it if you must.
The motherboard or PSU are also possible causes.
The bit that really confuses me is the whole "old" and "new" XP. It's all the same thing, so I don't know why you installed XP over XP to cure the issue that it didn't support everything. I'm not getting that. I could understand reinstalling it just because it's been a few years and may be starting to act funny, but functionally, it's the same exact thing.
Unrelated, but is there a reason you're not running SP3?
The first thing I'd check is the RAM.
If the motherboard has onboard video, try removing the GPU.
After that, try a clean install of an OS on the same hard disk (this rules out the HD and the OS). Make a new partition for it if you must.
The motherboard or PSU are also possible causes.
The bit that really confuses me is the whole "old" and "new" XP. It's all the same thing, so I don't know why you installed XP over XP to cure the issue that it didn't support everything. I'm not getting that. I could understand reinstalling it just because it's been a few years and may be starting to act funny, but functionally, it's the same exact thing.
Unrelated, but is there a reason you're not running SP3?