XP will not reboot

[HanoNymus]

I'm running XP on a P4 machine. The install is about one year old and it still works well enough not to motivate me to do a format, except for one thing: at some point, after many an installation/desinstallation the PC won't reboot when asked to. It (kind of) shuts down and just "hangs". I think it goes trough the entire shutdown process, except for restarting. When I want to shut it down it does so properly. But when I need a reboot I have to manually push the reset button (and it starts up fine).

Is this a messed up registry entry, file, setting, or what?

(Checked the bios, could not see anything relevant).

[M11]

Most likely you have a system service that does not want to terminate properly. If you feel comfortable with administrative tools, you might be able to find out which one. But an install that old could also be at the root of the problem; whether this problem is an isolated incident or normal windows decay is yet to be determined. If you have the time, just wipe, before we get a data recovery thread:p

[Qwertyman]

Shutdown XP Faster
When a user shuts down Windows XP, first the system has to kill all services currently running. Every once in a while the service does not shut down instantly and windows gives it a change to shut down on its own before it kills it. This amount of time that windows waits is stored in the system registry. If you modify this setting, then windows will kill the service earlier. To modify the setting, follow the directions below:

1. Start Regedit.
2. Navigate to HKEY_LOCAL_MACHINE/SYSTEM/CurrentControlSet/Control.
3. Click on the "Control" Folder.
4. Select "WaitToKillServiceTimeout"
5. Right click on it and select Modify.
6. Set it a value lower than 2000 (Mine is set to 200).

http://www.charliesources.net/nieuwe%20winxp/windows_xp_performance_tweaking.htm
try that