Ubuntu Software Center does not proceed from applying changes

I had the same issue too. However, I tried the following. Ran

sudo lsof /var/lib/dpkg/lock

From there I identified the PID of the process causing my dpkg to lock. Then I did

sudo kill -TERM <PID>

Next, I did a

 sudo dpkg --configure -a

and waited for the result... after that i did a regular

sudo apt-get update && sudo apt-get upgrade

Hope it will work for you too.

Make sure there isn't a dialog window somewhere that needs your input to allow the installation to proceed.

In a similar situation, you see, kill -9 worked for me. But then when I started Ubuntu Software Center again it was still stuck in the same spot. Until I closed all the open windows and saw that it was waiting for me to enter an answer. Duh. Software then finished installing.

Try to search for and terminate the /usr/bin/dpkg process:

Gabriel@UMWC:~$ ps ax | grep dpkg
 2058 pts/0    SNs+   0:00 /usr/bin/dpkg --status-fd 14 --configure -a --force-confdef --force-confold
 2061 pts/0    SN+    0:00 /bin/sh /var/lib/dpkg/info/nautilus-dropbox.postinst configure 
 2275 pts/2    S+     0:00 grep --color=auto dpkg
Gabriel@UMWC:~$ sudo kill 2058