What does Last.FM mean?
That's not normal. Take the card out to test it.
I have noticed my Mac won't sleep if I am running VLC. You might want to check what programs you have operating and see how sleep works with those programs.
Mate, you seem to have found the culprit, good work. I don't think it's all that unreasonable to expect a non-OSX compliant card to not work with OSX though...