If you want to know why wont avast open, you can follow the step given below:
1. Broken Avast Installation
2. Avast Antivirus Service Not Running Properly
3. Repair Avast
4. Restart the Avast Antivirus Service
5. Perform a Clean Install
Hopefully above steps will help you to fix the issue if not you can also follow our blog to see more on cannot open avast user interface.