I've seen this kind of thing fixed before, but this really depends on what is causing the system failure. Sounds like you don't feel like messing with it anymore, but if you change your mind you might try:
1. Open a command prompt and run chkdsk /r on the hard drive. This will check the file system for errors and the disk for bad sectors, repairing what it can, marking bad spots so the machine won't try to use them anymore. If you can't get that to run because it keeps rebooting or blue screening (if you changed that reboot setting), try booting into safe mode with a command prompt, then quickly typing chkdsk /r and hit enter, then "yes" when asked to run on reboot. If you got that far and it still hasn't rebooted, reboot it yourself. Chkdsk runs before the OS is fully loaded so it shouldn't reboot again while chkdsk is running (if it does, this is likely a heat issue or some other type of hardware issue). If you can't get that typed in fast enough before it reboots, you could remove the drive, connect it as a secondary drive to another computer and run it from there, then put it back in the original machine.
2. Run the XP system repair disk to repair any corrupt system files.
3. Reboot while holding your breath.
Not guaranteed to work by any means, but I have seen it resolve this type of issue.