1. Verify that you are entering your password correctly and check whether CAPS lock and NUM lock are on/off to ensure this is correct.
2. Check if your device might not have a network connection.
3. Check if your keyboard setting is correct. You can do this by simply testing your password in the username field or, in Windows 8, by clicking on the 'eye' so it becomes briefly visible.

If you have checked both things and you still can't log in, please feel free to contact us.