Start regedit from Run box and go to key
HKEY_CURRENT_USER\Software\Policies\Microsoft\Inte rnet Explorer\Control Panel
You will find a key named Homepage on the right. Righ click on it and select Modify. Change it from 1 to 0. Now you can modify the homepage.
Here 1 stands for hiding and 0 for unhiding.
Here is the scrrenshot
Otherwise you can use Spybot to lock/unlock your homepage.