If you’re installing Windows XP Service Pack 2/3 and it halts or hangs on you while it is allegedly “Checking Product Key”, you can fix it like so:

  1. Please go into the CMD prompt (Start/Run –> cmd.exe )
  2. Then type cd /d %windir%\inf and make sure we are in that directory.
  3. Then type ren oem*.inf oem*.old, it will go back to the prompt after giving you some error (Do not worry about it)
  4. Then type ren oem*.pnf oem*.old1, it will go back to the prompt after giving you some error (Do not worry about it)
  5. Then goto start – run – type “%windir%\inf” and you will see the files in the folder.
  6. Then find the file by name INFCACHE.1 and take a backup of it to desktop (by copying it to desktop) and delete the INFCACHE.1 from c:\windows\inf.
  7. Close all windows and reboot the computer to safe mode and start the installation of SP2 and it should go fine.

 

Sumber : http://www.twistedethics.com/2007/10/15/windows-xp-service-pack-2-halts-on-checking-product-key/