Cant quit Itunes

Hey,

I am needing to make software updates on my MacBook and the only way to do that is if every program on my computer is not active. However, my iTunes refuses to quit, even when a window pops up giving me the option to select "quit itunes" will not work. I have tried shutting off my computer and because iTunes wont quit i cant even do that.

Also, my iTunes wont open either, that's issue #2. So all in all, iTunes will not open or close for me.

If you know how to help me that would be great, thanks!