Most Win XP shutdown problems reported thus far have been that it reboots when shutdown is attempted. This may be a global symptom emerging from several distinct causes, because, by default, XP executes an automatic restart in the event of a system failure. Therefore, more or less anything compromising the operating system during the shutdown process could force this reboot.
Disabling the “restart on system failure†feature may permit the exact cause to be isolated: Right-click on My Computer, click Properties, click the Advanced tab. Under “Startup & Recovery,†click Settings. Under “System Failure,†uncheck the box in front of “Automatically restart.â€
USB Connections As can be seen from remarks in the Misc. Hardware Issues section below, several different USB-related issues can impact shutdown. One of the most concrete examples was a “reboot on shutdown†problem contributed by correspondent Rick Bross. If his several USB devices (PDA cradle, flash card reader, etc) were plugged into the motherboard’s USB ports, his computer would reboot on an attempted shutdown; but when, instead, he plugged them into an external USB 2.0 hub, shutdown went just fine. (This was with Win XP Professional SP1 on a Supermicro X5DAE dual Xeon motherboard. The same devices plugged into an Asus A7M-266D dual AMD 2000MP system on the same OS worked without problem.)
“Wake on†power settings Power-management settings that have the computer “wake†on LAN, USB, modem, or (for that matter) probably anything else may also trigger a restart after shutdown. Correspondent Simon Wei provided this tip after a friend of his found an old old Logitech USB mouse would trigger “wake on USB†after every Windows shutdown. Their solution was to remove that particular mouse and all worked fine. The principle is much more far-reaching than this one example