ITunes woun't accept my password.

When I try to buy a song the ITunes store will ask for my password but when I type it in it woun't even recognize it! No message will pop up but the sign in screen will just disappear like the password had been accepted but nothing will happen. I know I am using the right password and I even reset it to see if that would help but it still does the same thing. How do I get it to work again?!? (I'm working off a computer)