I upgraded to 2.2.1 a few weeks ago, and everything was fine until last week. Inexplicably--and I really do mean that, as I did NOTHING that can explain this--I lost my 'home' screen. I mean the default home screen with all the application icons on it. Now when I press the 'home' button, I'm prompted to choose from several homescreen apps I had previously installed--but the basic, default one is no longer listed as an option. How do I get it back?