Why can’t I set my internet home page to what I want?
It depends on “how” you can’t.
If you can change your home page and later it changes back to something else then you probably have spyware.
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If you can’t change your home page – the option is greyed out – then you may have spyware or if you’re in a corporate or other controlled environment then you may not have permission to do so.
In any case, spyware is the top suspect, so I’d run a spyware checker right away.