iTunes is not responding at all

I have the updated iTunes 10.5.1 and have been listening to it until yesterday. It appears to be open on my dock (little white button is next to the icon) but my library will not appear and when I click on the icon the itunes menu does not show up at the top of the screen. I am running Mac OSX 10.6.8 and all my software is updated.

I have restarted my computer a couple of times and it still won't respond.

Any suggestions?

Thanks,

Karen