Try running spybot, check start spybot > click on tools in the left hand column > ie tweaks > under miscellaneous locks check that the "lock ie start page" and "lock ie control panel" boxes are unchecked.
You may have to be in advanced mode to do this.
Use the mode button in the toolbar to change if required.
or run Regedit and delete the following keys (if they exist - but copy/export them first!!!)
; lock home page for all users
[HKEY_LOCAL_MACHINE\SOFTWARE\Policies\Microsoft\Internet Explorer\Control Panel]
"HomePage"=dword:00000001
; lock home page for current user
[HKEY_CURRENT_USER\Software\Policies\Microsoft\Internet Explorer\Control Panel]
"HomePage"=dword:00000001