Have been using Avast Pro for a while with good results until this morning when I had to do a system restore–not connected with Avast Pro. Afterwards, Avast Pro has a little X on it and everything I do appears to go nowhere. I realise now that perhaps I should have turned Avast off before I did the system restore. But what should I do now?
Welcome to the forum. :)Go to Add/Remove, select avast! scroll down and select repair.
Once it finishes the repair, reboot your system.
When the system comes back up, let us know if that’s cured the problem. 
Please follow Bob’s advice.
If the repair doesn’t work continue here:
https://support.avast.com/index.php?_m=knowledgebase&_a=viewarticle&kbarticleid=1050
https://support.avast.com/index.php?languageid=1&group=eng&_m=knowledgebase&_a=viewarticle&kbarticleid=1049