Password blocked in terminal

Tried to unlock the hosts file, accessing it through "Terminal". When using "Terminal" and typing in a "sudo" command the following warning came up;

WARNING: Improper use of the sudo command could lead to data loss or the deletion of important system files. Please double check your typing when using sudo. Type "man sudo" for more information.

To proceed, type your password or type Ctrl-C to abort.

Password: (after the colon, there is a dark vertical rectangular cursor, with a white circle in the middle).

I am unable to type any thing at all after the word "Password".

What do I need to do to get past this block and get access to the host file and get it unlocked.

Thank you for any help.

15" Macbook Pro OS X 10.6.8 Yosemite