Hi I have no experience in down loading apps But...
Have you tried shutting down and a fresh boot up. Make sure caps lock hasn't been locked, or num-lock switched off at some point.
I cant see any one else having this problem on line, but there is a way to reset the password in you-tube, seems to be a lengthily process though.
As you type the password in does it show ....... or can you actually see the password name as you type it in.
if its ....... make sure each time you hit a key for your password or number it is showing a . as you may have a stuck key etc.