[ubuntu] switch user

view full story

http://ubuntuforums.org – I'm using ubuntu on virtualbox. I'm trying to learn terminal commands. My problem is: I cannot switch to a different user (that i created using useradd). I can only switch from my user account to root and vice versa. When I try to type su bob, it would prompt for a password, then I enter the password. After that it would just show a new line with "S" displayed at the start. The same thing happens to the other users that I created as well. Please help. (Hardware)