MacOSX El Capitan: admin password only working from login screen
Open Textedit and type there your password
to check which problem might be yours:


typing errors,
bad repeating tuning,
num lock,
keys problems,
session configuration error.


If you think you have a typical problem with just the login window,
just configure your login so as to take advantage of your name
part of the login window to check how your keyboard and your software
are behaving.
Configure System Preferences &gt; Users &amp; Groups as follows:


Within the Name: part of the login window, type all the characters
contained in your password and check for:


bad repeating tuning,
num lock,
keys problems.