I had experienced two possibilities on rebooting.
One was you have two Firewalls on your PC particularly if you have the ZoneAlarm Pro 4.5 or higher as it would not get along with any other firewall. In other words, your PC only needs the ZoneAlarm Pro 4.5 or higher and nothing else. The other cause could be you have a seperate video card installed and your motherboard has its on board video card. Therefore, two video cards crash to each other resulting rebooting.
Once and for all, have Windows XP re-installed as I always suggest people to do that. Re-install Windows XP will solve every problem in your PC because it will re-format your hard-drive. I do that very often because my Windows XP Professional CD is a jewel, it does not require license keys or anything. All it takes is lots of time on one Saturday night till Sunday morning.
But I would guess the rebooting of your case is the firewall or anti-virus crash with another firewall or anti-virus. You have to decide which one to be removed. When you removed a program, also note you have to remove that program from the add/remove categories of the " Control Panel " as well as the C drive-program file. Inside that " Program file " of the C drive, you will see the same program as you see in the add/remove categories of the " Control Panel ". Have that program removed too.
Asking this question for my sister she went and got an update from windows web site after the update finish it said reboot computer before the update will take. So she did now all her computer do is keep rebooting and rebooting
Windows xp home
thanks for the help