1) You didn't mention what brand of motherboard you're using, nor
whether or not any of the hardware is new to the system.
2) Was the system working before you installed XP, or is this a
completely new system?
3) If it was a previously working before you installed XP, did you
"upgrade" from a previous (old) version of Windows, or was it a
*** format/install?
If you're dealing with new hardware:
A) Make double-damn sure the heatsink is installed *correctly* on the
CPU. Heat buildup will cause problems.
B) AMD CPU's require 300W (or better) name-brand PSU's. Get an
Enermax if you're convinced it's the power supply.
C) Make sure that there aren't ANY cards in the PCI slot immediately
adjacent to the video card. XP uses ACPI, and that can aggravate IRQ
sharing issues.
D) Remove everything except the drives, the, video card, and ONE
stick of RAM. Reformat your hard drive, and re-install XP. Then, add
the memory back one stick at a time. If the system still appears to
work, re-insert the sound card, and then then ethernet card.
If you're NOT dealing with all new hardware, it might simply be that
XP doesn't like something in your system (and probably only when it's
installed in your system). If you followed the step "D" stuff and it
still doesn't work, you should be able to easily identify the
offending hardware.