How To Activate Windows XP License Key

My Windows XP ask for activating, and worse, I don't have the license key. I found that this problem could be solved by editing registry entry.
-Open regedit: From Start, Run enter regedit.
-Backup your registry first! Click File, export than specified where you store your current registry.
-Find this entry: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\WPAEvents. Doubleclick OOBETimer, replace data, see capture.

-Right click on WPAEvents subkey, click permission.
-Select SYSTEM, check Deny full control, click OK.

-Close your registry editor.
-Verify new configuration, click Start, Run, type: %systemroot%\system32\oobe\msoobe.exe /a.

-Click "Activate on the phone", "Change product key".
-Type: THMPV - 77D6F - 94376 - 8HGKG - VRDRQ
-Click Update.
-Click Remind later.
-Restart Windows.