Amarok refuses to play *.ogg's. Now I'll be the first to admit if I broke it myself, and it would not be the first time either. But in this case I just don't know what went wrong. I don't believe 'the computer' did anything either. It's just plain weird. One day it works, the other day it doesn't.
The package manager says everything is in place. But Amarok claims it can't find the demux plugin??