Tomnjerry,
Make sure the power settings in Windows XP are properly setup. You can check this by clicking Start, Settings Control Panel, clicking on the Power icon. In the Power Options Properties window make sure the computer is set to power off when you press the power button (or however you wish to the computer to turn off when pressing the power button). In addition you may wish to enable hibernation mode under the hibernate tab.
If this is set to power off it’s possible that your computers ACPI may conflict or have problems with Windows XP. Check your power settings in CMOS setup. Usually you can enter CMOS setup by pressing the F1 or F2 to enter setup when the computer is first booting (these keys may be different). Within CMOS check for power schemes, and attempt to temporarily disable any value that is enabled.
Finally, if you are still encountering power related issues you may want to check with your computer and/or motherboard manufacturer for any BIOS updates that may need to be added after upgrading to Windows XP.
