Computer totally up **** creek

Hi. I have been having tremendous trouble with my computer recently. It all
started around Christmas time. I used my computer on Christmas Eve, switched
it off and didn't come back to it again until Boxing day, only to discover
that it would not start at all. After a bit of experimentation, I discovered
the power supply had packed up for no apparent reason (had it less than a
year and it's plugged in to a surge protector.)
I put in a 300w PSU (the previous one was 400w) temporarily but discovered
that I was having new problems with my computer randomly restarting every so
often, but I put this down to the lower wattage PSU.
I decided to reinstall Win2K anyway and so, for a number of reasons, put the
hard drive in a different computer and formatted it and installed W2K and it
all worked fine. Until, that is, I put the hard drive back in the original
computer (with new shiny 550w PSU) and it refused to boot. Kept getting a
BSOD saying innacessible boot device etc. etc. So, I tried reinstalling W2K
again. It gets as far as formatting the hard drive but as soon as it starts
to install windows I get a BSOD saying something about a "stop error" and
"if this is the first time you have seen this message reboot and try again
etc. etc."

Basically, I'm pretty much out of ideas. I don't think it can be the hard
drive because it worked in the other computer but then I don't see how it
can be the motherboard either. Any suggestions?

Oh and if it helps here is my hardwa

Athlon XP 2400+
1Gb DDR RAM
Epox EP-8RDAN motherboard
80GB Maxtor Hard drive