Found this on another forum - might be worth a try, but please don't skip step 1, in case you need to restore the registry:-
Click Start->Run, type "regedit" in the Open box, and click OK.
1. Make backup copy of registry (File > Export)
2. Navigate to HKEY_LOCAL_MACHINE\System\Setup"
3. If there is any key or values named "FactoryPreInstallInProgress", right click and delete it.
Reboot, and hopefully that should do it.