As said in title. Unable to open the gui or end the running application.
A reboot did not resolve the issue
Im running win 10
There hasn’t been a update today.
That depends on the customer and how he/she updates. 
Repair Avast:
Control Panel> Program and Features (Add/remove program)>Select Avast> Select Repair. Reboot when completed
https://www.avast.com/faq.php?article=AVKB204
If Repair doesn’t fix the problem, try the following:
Clean Install of Avast:
https://goo.gl/4Ptzkf
If you need additional help with the Clean Install, watch this:
https://youtu.be/p-h3myRD51A