How do I correct a Windows XP installation that has become deactiviated?

A. XP contains a new feature called System Restore that restores the system to a previous configuration point. Should you restore your system to a point before you activated XP on your computer, the OS will forget that you activated it and you'll need to reactivate XP. If the system restore point is past the 30-day grace period that Microsoft allows for activation, you'll have to activate XP immediately.

The only workaround to reactivating your system is to perform the following steps:

The above procedure will work only if you've made no significant hardware changes.