mchain
9
Assuming you’ve just had your system in due to the registry hive problems, and it was the repair guy that fixed that issue, personally I’d go back to him/her to fix your new issue with avast! 8 running on Windows 8, I assume? This should be under some sort of warranty, so it should not be about having to spend additional monies to fix what’s wrong here.
Only he/she knows what they had to do to get your system running properly again, so… I’d also have the repair guy look at why you’ve issues with windows updates as well.
Not to put off your request for help here at all, but seems the above is the best course of action given that you just had it repaired, if that is indeed the case. 
You can, come back here again, if you wish, if your repair guy either refuses to assist you or cannot fix your issue(s).