Behaviour Shield still turning off

Today my Avast, (v 17.9.2322, Windows 10 64 bits) started behaving strangely. On reboot it takes a very long time for Avast to start up. When it does, Behaviour Shield is turned off and it is impossible to turn it back on. This problem has been around for a long time and it is still not resolved. Can someone from Avast please advise.

Repair Avast:
Control Panel> Program and Features (Add/remove program)>Select Avast> Select Repair. Reboot when completed
https://www.avast.com/faq.php?article=AVKB204
If Repair doesn’t fix the problem, try the following:
Clean Install of Avast:
https://goo.gl/4Ptzkf

This happens to me too - takes ages for avast! to turn on then the behaviour shield is off. Doesn’t happen all the time but it will happen every time I log on for a few days, then it stops.

I have Windows 7

I’m not very computer literate either so don’t even know what a behaviour shield does! But if it’s supposed to shield the computer and isn’t doing so, that seems a bad thing!

https://forum.avast.com/index.php?topic=201143.msg1431155#msg1431155