If you mean it constantly restarts, first run a virus scan and be sure your
antivirus software is up to date. Since the machine is constantly doing
this, see if you can run it from Safe Mode. Boot the system, start tapping
F8, at the menu choose Safe Mode.
If the system comes up clean, place the XP CD in the drive, when the setup
screen appears, select, "Check System Compatibility." Do not consider
anything that it might designate as an issue as too small to be the source
of the problem.
XP by default is set to reboot on certain errors. Go to Control Panel, open
System, go to the Advanced tab, click Settings under Startup and Recovery,
remove the check from "Automatically Restart" under system failure. This
will cause the system to blue screen instead of restart and the message may
give a clue as to the source of the issue.
Also, check Event Viewer, open Control Panel, go to Administrative Tools,
open Event Viewer, look for errors that correspond to when the error
happened, double click, the information within may give a clue as to the
source of the problem.
