I have a different problem.When first time I used ubuntu old to new in every version I can easily type password in terminal after sudo command.But now a day I can't because In terminal after sudo command in password i can't able to type any thing like char or number ,but just in password other part in terminal I can type. Now,probelm is there that it don't show password means not that in terminal password is in hide mode.Every time I type in after that it show me" sorry,try again" error message after three time wrong password means empty password it's again come into first position. For solve this problem I used old to new version of ubuntu also format it many time but same problem occured. Please help me because without terminal password I can't install anything.
I know this may sound stupid, but have you tried turning on/off caps lock?
Also (it's hard to tell from your english, sorry) but it sounds like you can't see the password. This is normal, you aren't supposed to see anything. Keep typing you password and press enter :)
EDIT Also, have you tried swapping keyboards? Maybe the keyboard is the problem.