Repair Avast:
Open the Avast User Interface > Menu > Settings > Troubleshooting > Repair App. or,
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:
If your Avast settings are not the default settings and you want them restored after the Clean Install, follow this before removing Avast. https://goo.gl/TXjM7h Clean Install of Avast: https://goo.gl/4Ptzkf
If you need additional help with the Clean Install, watch this: https://youtu.be/p-h3myRD51A