If you have A previously created restore point in your system, you can use System Restore to undo registry changes in in Windows XP

Use Windows Key+R to get a Run box

In the Run box, type

%SystemRoot%\System32\Restore\Rstrui.exe

and then click OK.

On the Welcome to System Restore page, click Restore my computer to an earlier time (if it is not already selected), and then click Next .

On the Select a Restore Point page, click the system checkpoint.

In the On this list select the restore point area, click an entry that is named “Guided Help (Registry Backup),” and then click Next.

If a System Restore message appears that lists configuration changes that System Restore will make, click OK.

On the Confirm Restore Point Selection page, click Next.

System Restore restores the previous Windows XP configuration and then restarts the computer.

Log on to the computer. When the System Restore confirmation page appears, click OK.