I'm so embarrassed to even admit this, but here goes anyway.....
It's been quite a while since I've updated Avast. I had to uninstall and re-install it before with this same problem, which is pretty much being unable to update virus definitions or the actual software. The update starts up, but goes between status bar and an "unknown error" notification until it gives up. Now, I thought it was TinyWall at first (long story there....boils down to my laptop suddenly hating Comodo Firewall and getting nothing but errors trying to start it up..) and I called myself making sure to allow each process related to Avast. I could be missing something.
I'm currently updating Windows as I speak, seeing if that will help. I'm using Windows 10.
Aside from TinyWall, I use SpyBot and ASC 10 Pro.
If anyone needs more specs (you probably do, and I'll give you what you need...) let me know. I'm trying everything I can before giving up. And...honestly, I would rather not give up on Avast.
Thank you.