On my laptop, I have an install of the Windows 8 Beta that is an upgrade from Windows 7. The Metro "Files" browser worked perfectly for a while and then it suddenly stopped working. The app will pop up for a split second and immediately close, meaning I can't manage any files within Metro (set the Lock Screen from PC Settings, change my account avatar, stuff like that). This issue came up when I tried un-installing Pew Pew by manually deleting its files and deleting as many of its Registry entries as I could. I'd guess the issue lies somewhere there but I don't see how that would cause problems.

Does anyone know of a fix or will I have to run a clean install of Windows 8? I still haven't figured out how to un-install Pew Pew by the way and it's still in my Start Screen, just invisible and un-launchable...

Why don't you try upgrading from Windows 8 to Windows 8 itself? I've tried such things a couple of times with XP, Vista and 7. It just replaces all the system files. I many times "upgraded" Windows 7 Home Premium to itself. It works, problems are solved, I don't have to do a clean install. About "Pew Pew", well, it's a funny app. I always irritate my sister by launching it in front of her. That sound of "Pew..." really bugs her. Anyway, I'm not trying to influence your decision. Doesn't that uninstall option (on right clicking the tile) work?