This is from a Microsoft article: How to troubleshoot hibernation and standby issues in Windows XP
If your computer does not resume from hibernation or from standby, restart the computer
If you cannot resume your computer from hibernation or from standby, press and release the power button to restart it. By default, ACPI-compliant systems are configured to shut down when the power button is pressed and released. If you have an older system that has a reset button, press the reset button to restart. If the computer does not restart when you press the reset button, press the power button to turn off the computer. If you have an ACPI-compliant system that does not shut down after a short time, press and hold the power button until the system turns off. The system usually turns off in about four seconds.
If the same problem occurs after power off then do it again only this time Press F8 to get to the Advanced Boot Options Menu. Select Last known good configuration that worked
, see if that helps.
If not do it one more time and go to Safe Mode. Login as Administrator (no password unless you added one. If so use it). Use System Restore to go back to a time before this occurred.
Start / Run / Accessories / System Tools / System Restore