dpkg was interrupted, you must manually run

You strictly need to open a Terminal from the menu Applications->Accessories->Terminal and type:

sudo dpkg --configure -a

give your user password when requested, you don't see nothing when you type it, then press enter.
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But to fully check and upgrade your system using terminal using command line,
open a Terminal from the menu Applications->Accessories->Terminal

Tip: right click with mouse on the terminal title caption and select the item "Always on Top" doing this you will force the terminal window to stay on top of the other windows and you will find very easy to copy single row from this web page into the terminal...
Something more about using the terminal https://help.ubuntu.com/community/UsingTheTerminal

Then type or better copy and paste a row a time then press enter:
(Tip: select the single row to copy then right click into the terminal and to quick paste click with middle button of mouse )

sudo dpkg --configure -a
sudo apt-get -f install
sudo apt-get --fix-missing install
sudo apt-get clean
sudo apt-get update
sudo apt-get dist-upgrade
sudo apt-get clean
sudo apt-get autoremove

then please reboot your system, type

sudo reboot

give your user password when requested, you don't see nothing when you type it, then press enter.

Hope this helps

I got the second line and it worked away for 20 mins or so then brought up an end user license. There is an OK at the bottom but nothing happens when I click it. Then I get the same message as before.

sudo dpkg --configure -a

Should fix you up nice

I've tried that already and it didn't work, hence me being at a loss. Anyone else had this? Or is it just me

"There is an OK at the bottom but nothing happens when I click it."

Use arrow keys to get to O.K. and hit enter.

Good point. Thanks, worked a treat.