Computer Help and Support

There are infections that will block downloading of popular anti spyware programs.

You could try this instead.

http://www.bleepingcomputer.com/download/adwcleaner/

That is actually a much faster stand alone scan that should not interfere with antivirus. That said it doesn't do as good of a job as malwarebytes but it does sometimes get things malwarebytes will miss. When I work on client machines I typically run both.

And again any time the Home page changes with no input from the user that is usually a sign of some sort of infection. It is possible that the home page itself was changed by the company that owns it and it just looks different.