There may be different reasons behind, if you cannot open avast user interface.
Here, you are because you are looking for "avast antivirus not opening". Now we have tried to find out the solution for this...
Solution 1: Repair Avast Antivirus
Solution 2: Restart the Avast Antivirus Service
Solution 3: Perform a Clean Re-Install
Hope you have been able to fix the issue in a very easy way, however, if you struggle to fix the problem then you can call 24*7 our expert available for brother printer showing offline, allow chrome to access the network in your firewall or antivirus settings mac