I have Avast premium, until yesterday I never had a problem. Today I can not open it but when I check my APPs it says it is loaded.
If the Avast app becomes outdated, then it might show some problems when opening the app. So, ensure that the app is up to date. Plus, many other issues, like firewall interruptions, system errors, software issues, settings, and others, can also lead to the problem. So, you should consider these points and take additional help if necessary.