Apple id disabled???

If your account has been disabled then you might be able to re-enable it via this page : http://appleid.apple.com, then 'reset your password'

If it then works on your computer's iTunes but not your iPad / iPhone / iPod Touch then try logging out of your account on the device by tapping on your id in Settings > Store (Settings > iTunes & App Stores on iOS 6) and then log back in and see if that 'refreshes' the account on it

If that doesn't fix it then you might need to contact Apple : http://www.apple.com/support/itunes/contact/ - click on Contact iTunes Store Support on the right-hand side of the page