This article describes situations in which you must reinstall Service Pack 1 (SP1) for Windows XP. With some Microsoft operating systems such as Microsoft Windows NT you must re-apply the latest service pack after you make a change to your computer. Although you do not have to do so in Windows XP, there are a few situations in which you must reinstall SP1 for Windows XP.

Reinstall SP1 for Windows XP in the following situations:

After you perform an in-place upgrade (reinstallation) of Windows XP.

After you perform a repair of Windows XP.

After you use System Restore to restore your computer to a restore point that was created before you installed Windows XP SP1.

After you upgrade from Windows XP Home Edition to Windows XP Professional Edition.

When to Reinstall Windows XP Service Pack 1