You probably have something that is locking your home page. This can be some sort of malware which you can try to detect with AdAware click here or in extreme cases with HijackThis click here. It can be a feature of some computers wher the maker wants you always to use their own site as a home page. The home page is often locked by a registry entry. If you're comfortable with the registry have a look at Hkey_Current_User/Software/Microsoft/Internet/Explorer main/Start Page. An alternative is to use Mozilla Firefox instead of Internet Explorer click here.
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