Itunes wont let me sign in

I have atttempted signing in to my itunes account since it keeps popping up on my computer, yet it doesn't allow me. I have changed my password and have tried typing it in correctly several times. It works perfectly fine on my phone yet on my computer it keeps annoyingly saying it is the incorrect password. I have tried it several times and don't know what other way to make it work. Suggestions and help please?!