There is no music playing at all in my game. I have checked the Music folder and all the music files are still there in the right place.

I have the music set to full and still nothing. Sounds and stuff work fine, just no music.

The music for the Bethesda screen works ok, but the main menu where you choose to load, save, options etc has no music and neither does the game while playing.

Anyone have any idea what could cause this? It just started without any warning and always used to work fine.

add/remove any new/old software?

Try installing the klite basic codec pack. (uninstall/reinstall if you already have it) Make sure it is set to repair broken codecs, and have ffshow ignore oblivion, audio, and video.

How do I tell if I have it already or not?

Should show up in the add/remove programs applet in the control panel. Or, whatever it is called in the newer operating systems.