You may see something in the Action Center that says something like 'Turn on Avast' and you check Avast. The protection is on! How to fix this? This is caused by Windows not realizing protection is on, so a real easy reboot of the active protection shields of Avast should fix your Action Center good as new.
1. Go into Avast's user interface
2. On the side, click on Settings
3. In Settings, go to the 'Active Protection' tab.
4. Turn off all the shields. It will ask you how long. I don't think it matters what you choose there, because we are restarting the shields afterwards anyway.
5. After all 3 shields are turned off, Click on OK.
6. Go back to Home and it should say something like 'You are unprotected!'
7. Next to that, there should be a button called 'Resolve All'
8. Click that button, and all the shields will turn back on. Your Action Center should no longer say to turn on the antivirus
If I am wrong, feel free to tell me! I've just started using Avast.