For many computers, a reinstall of Windows XP (even if its on the same PC) requires re-activation with Microsoft. Some versions of XP require you to actually call Microsoft after a certain number of activations have already been performed to get it activated again. This howto shows how to bypass all this by backing up your activation files.
Backup Your Activation Files
You need to make a copy of and save on CD two files in your Windows\system32 folder. The files are wpa.dbl and wpa.bak.
Restore Your Activation Files
If you need to restore your activation files after a fresh install boot your computer in Safe Mode by pressing F8 on your keyboard repeatedly while the computer is booting up.
Once your computer is booted in safe mode, rename the current wpa.dbl to wpa.nonactivated and wpa.bat to wpabak.nonactivated in the Windows\system32 directory.
Please Note: In order to view or change a file’s file extension (.dbl) you might need to open My Documents, click Tools, select Folder Options, click the View Tab, uncheck Hide Extensions For Known File Types.
Copy you backed up activation files to the Windows\system32 folder.
When you restart your computer, Windows XP should be activated.