Regarding Dell MusicMatch Jukebox -- this info is from MusicMatch's support (but not the exact language) ...
When using the Jukebox and you have a problem that causes the Jukebox to have to close, then even after restarting your computer, you will not be able to open the Jukebox as the first program you use.
SOLUTION:
When Jukebox stops working, restart your computer, open any other program (such as a text file, a game, whatever), then open Jukebox.
 
I don't know anything about *why* Jukebox is this way; I know only that this does work -- and Jukebox shuts down on me regularly, so I've used the solution many times.  (I use MusicMatch Dell Jukebox 10; Windows XP Service Pack 2; McAfee Security Center; Dimension 2400.)
 
Hope this helps.