What's happened to my Windows 7 account?

Solution 1:

I don't know if Window Updates caused this or not, but I found the fix.

In the registry, I went to HKEY_CURRENT_USER\Volatile Environment. The AppData key's value was, literally, %APPDATA%. I changed it to %USERPROFILE%\AppData\Roaming, rebooted, and everything is working again.

I found the solution in Nihir's post here.

So, yes, basically, it was an issue with my user profile, as Windows no longer had a valid value for the %APPDATA% system variable.