Try typing sudo instead of su.
When I type su I get:
su: Authentication failure
or something along those line ... But when I do sudo it works.
So it would be like this (using lspci as example):
name@computer:$ sudo lspci
(sudo) password for user:
Enter your password, and you should be set. Note that when you are typing the password, no letters or asterisks (*) will show up. It will remain BLANK as you type.
You replace lspci with any other command/options you want to run as root.