This hardly falls into this category, but either way, can you type into any other text fields (ones that you can see the characters) without any problems with the output? Have you tried restarting your PC, or even using an on-screen keyboard to enter it in? You can also use the old "I forgot my password" route and try changing your password.
If none of that works, I would either guess that you are typing the password wrong or someone altered your account.