can't enter password in terminal

I think you need to setup a password for the account you are logged in with.

In the system preferences there are some options that can only be changed if you click on this icon:



If you don't have a password it is not able to unlock when you just type in nothing.

 

Are you sure you're using an administrator account?

 

also, when you type your password in Terminal, nothing is displayed on the screen - no asterisks, no cursor movement, nada. Just type the password and press enter.

 

dwfaust is correct - When you are asked to enter a password in the terminal, no characters are displayed as you type in the password.
There can be some uses for a blank password, so when you see a password request, all you need to do is press enter.
However, sometimes the blank password is not a good idea, because (as you have discovered), you may find that a blank password is not suitable when a real password (with actual characters) is needed, and a blank cannot work.
You will find that some parts of the system will not let you use a no-character (blank) password.

Think of it this way - a blank password (no characters) is NOT the same as no password. Even the blank means that you still have a password, it just has no characters. … a-a-and, you can't enter a password that has no characters.
So, in certain situations (and with some applications) a blank password results in an error - and the only way to correct the error is to add a password for your admin user account.