Question: I am new to Ubuntu, and I have just installed Ubuntu 12.04 on a computer. I am using an automatic proxy server. When I select a software package to install and input my password, the progress icon displays for a few seconds, and then it stops. I tried to install different programs, and I always had the same problem. I can browse the web with Firefox, so I know I have a network connection. I do not see any errors or anything. What should I do?

Answer: 
Just use synaptic package manager, even though it's not as fancy as the software center. To install it type: `sudo apt-get install synaptic` in the terminal.
I had the same problem with software. It's probably a permission thing. 

On my menu the command to open uses software-center with pkexec, which command without parameters defaults to superuser. It seems to have issues.

By altermint the menu command to gksu software-center I found it worked and installed programs with no problems.