"mimboot.exe" seems to be the offending startup program: I started
having this "shelliconhiddenwindow" problem after installing MMJB 10
too. I contacted MusicMatch tech support and they had me uninstall and
reinstall MMJB 10. That did not help, but in the process of doing
this, I happened to check the Windows task manager and found a process
running named "mim.exe" that was using 50% of my CPU time! This was on
a Dell 8300, 3GHz machine. This led me to finding the only MM startup
file I could find on my system called "mimboot.exe." I turned this off
in msconfig and the problem went away after restarting, but ONLY AS
LONG AS I DON'T RUN THE MMJB 10 PLAYER!! When I run the player,
mim.exe starts again and won't shut down unless I turn it off in Task
Manager or reboot the computer. I gave all this information to MM tech
support, but haven't heard anything back yet.