Windows 7 Professional, Windows Media Player that came with it. All Windows updates.

So something is wrong with your machine or account or whatever. As all settings and libraries are user dependent, I'd start with making a new Windows account and start all over with WMP there.
If the same problems arise there your options seem to be:
1. Clean install of Windows 7
2. Use another media player, like VLC player (free).

Kees