So I downloaded the free, ran the install and it got all the way to step 7 then shuts off. It does not appear to be installed, as I have no icons anywhere. I’ve deleted downloads and redownloaded, rebooted, ran the hash utililty, and still doesn’t work. Any ideas? I’m slightly better than novice, but not a pro so use plain language and be patient 
What OS (operating system)?
What version of avast? Free, Pro, AIS, Premium? Is it 18.5.2342?
What version of operating system? SP (Service Pack)?
Did you use the online installer and remove the old a/v first?