XP locked me out of Internet Options

– I have XP Home edition.
– My account (the ONLY account)is an Admin type of acccount.
– I cannot get into Internet Options in my browser, nor can I view Source on any website(even my own)
– I get the following message:
This operation has been cancelled due to the restrictions that have been placed on this computer. Please contact your system administrator.

I can get into Internet Options if I boot in Safe Mode but I shouldnt have to do this. How can I undo whatever has been ‘done’ ?
(No, we have no teenage kids at home to blame)