Ubuntu Software Centre is stalled installing a package and I can't install anything else

I am very very new to Linux and Ubuntu having only installed it today. I was trying to install an application using Software Centre and the installation stalled and is now stuck - it has been "Applying Changes" for hours. I can't clear it and anything else I want to install queues behind it and wont install. Any ideas on what went wrong and how I can recover?

Try killing the dpkg process. Open the terminal(Ctrl+Alt+T) and type sudo pkill dpkg. Then try sudo dpkg --configure -a

It often works to close the Ubuntu Software Center and any open terminal window, and then reopen the Ubuntu Software Center. The package installation will continue to install the list of queued packages from the same place where it left off.

If that doesn't work, a stronger way to fix the problem is to close all open windows, logout, log back in, open the Ubuntu Software Center, and queue up the packages to be installed again.

I should have said I did the obvious things - like closing Software Centre and everything else and reboot. The suspended install was still there.

After more research I started trying to kill processes through the terminal window (didn't think I'd need to do that so fast - my unix is very very rusty) - after much research I came across two commands

sudo dpkg --purge --force-all astah-community
sudo apt-get install -f

I then rebooted for about the 25th time and the problem was gone.

I suspect the issue arose when I was trying to install third party drivers for a Epson Artisan 725 printer, which I still need to resolve - but that is another issue.