AVG User Interface Won't Open

For the last four days I have been getting a pop up message that the AVG UI cannot open but that I am still protected.  I am unable to manually open the UI.  What is more, my PC Tune Up has vanished.  It is still there on my main menu and as an icon on my desk top but they are both inactive.

How do I recover them to make them fully functional once more?

Hello Graham.
We regret the inconvenience caused and we're here to help. Click this link for instructions to resolve the user interface issues concerning AVG Internet Security and AVG TuneUp.