My Itunes on my macbook will not close

Hello, my Itunes won`t seem to close. I try to force close it because it`s annoying me, but it doesn`t react. This "log in" with apple ID window pops up. When I type in my apple ID (which is the correct one), the window pops up again and still tells me to log in. I don`t know what to do and I am getting frustrated. Have anyone else experienced the same problem? please help.