Archived from groups: microsoft.public.windowsxp.help_and_support (More info?)
Run Disk Cleanup (with your browser off) to delete temporary internet files.
Go to My Computer icon, do a right-click, then select Properties. Select the "Advanced" TAB and in the Startup and Recovery section (3rd block, near bottom) click the "Settings" button.
At System Failure block, "Un-check" the "Automatically restart" line. Apply change, make clean exit.
This will prevent a "reboot on error", and will also show (when you have Windows exception) the error code and its description.
IF a STOP error occurs, write down its number and complete description and follow up on fixes.
I'd suggest you insure there is no severe overheating of your pc. Then run a hardware diagnostic to check the RAM memory.
Be sure to have good pc ventilation & adequate cooling. Beware overheating.
If you suspect a heating problem, first be sure there is sufficient space all around the pc case for air circulation. Be sure there is nothing blocking any air intake slots. Take a look at the power supply fan (usually in back of the pc case) to be sure it is not blocked with dust & gunk, and that it is turning when power is on.
With pc powered off, and with adequate antistatic protection, look inside your pc case. Remove all dust.
Very carefully....turn power on & observe that all internal fans are running.