is windows xp all up to date with service pack 2 and hotfixes etc.? click here
what does the error say exactly if you can remember?
try having a look in event viewer and see if anything is reported at the time and date that you had this error. click 'start/control panel/administrative tools/even viewer' and then click on the 'system' and 'application' tabs and look for errors listed with a red x.