First, find out if your PC hardware is working:
1) can you boot to the BIOS?
2) does MEMTEST pass?
www.memtest.org (one full pass)
3) Optional test: can you boot to an Ubuntu DVD? (this tests everything but your hard drive)
You can burn an Ubuntu DVD on a different computer for free (though it asks you to pay) from the Ubuntu website. Just boot to that and run (not install) it from DVD.
RESTORING XP:
If your hardware works, then normally you do a System Restore unfortunately since you keep crashing this is likely not possible. If it was a hardware issue and you resolve it then Google how to do a System Restore to the last restore point (assuming you have one).
*Another alternative is to restore the Hidden Image, but if you installed XP yourself you won't have one. That's on pre-built systems. If you have one, and restore it, it will replace your current XP setup so everything is gone.
I would need more feedback regarding my tests to help further.