system
10
Ok, finally fixed it after what seemed like forty reboots and two system restores. I found that: I had to run the Avast uninstaller many times in Safe mode, uninstalled COMODO firewall, removed SpyBot (very difficult as disabled the startup items tray element and it wants to reinstall) - the key thing to look at here is to look at Windows Defender and see if it will work for ‘real time protection’ when Avast has been uninstalled - if not then SpyBot is still being loaded in some shape or form (or you have something else acting like AV - could be parts of COMODO firewall) - the clincher here was by chance that Win 10 complained that both Defender and SpyBot were off, so I chose Defender only.
At the point of Defender working and Avast not installed I did create a new restore point just in case.
And… after installing Avast then Chrome failed to run so had to reinstall.
And… the Avast cleaner does not work in Safe Mode after downloading if you just boot to safe mode (Windows key + shift + click on power button), probably down to some Win10 program checker. You have to run the cleaner outside of Safe Mode and follow its instructions and get it to restart into Safe Mode then it will run. After running, run again just to be sure no other installations.
I hope these notes help you. And thank you to everybody who replied and helped me :).