error conecting wireless
 

I am using ubuntu 12.04 . whenever i tried to install a theme in terminal it shows "unable to locate package" , and for some other commands its shows "file or directory not found". now my wireless connection is not working. when i first install ubuntu 12.4 i had to restart my laptop to connect through wifi when i turn wireless on, now its not at all connecting. what can i do?
sometimes my lap got stuck wile updating software showing "applying changes"
How can i resolve the problem?

type the following command in a terminal