The most common reason for log-in problems is that a computer's keyboard CapsLock is accidentally set to type all capital letters. Capitalization matters in passwords.
If you accidentally turn your keyboard's CapsLock setting on, all letters will be capitalized.
You can check your CapsLock setting by typing alphabetic letters in any program that shows what you're typing.
Press and hold the Shift key and then press an alphabetic key once (and then release the Shift key) in order to type that letter in a case different from the current CapsLock setting.
Most keyboards change the CapsLock setting by pressing that key again. Typewriters used to call the key "ShiftLock".