This might happen due to several things. I suggest you try to log in to your account on the official website. It is advised to do this from a computer. If you can't do this, try to recover your Account name or your password. It's possible that you can't log in due to incorrect information. If you had no problem in connecting to your account, go to Menu in your device > Settings > Application > All tab, select the application that won't allow you to log in to your account and tap Clear Cache. After you did this, try again. Your problem should be fixed.