welcome to the forum.
do you have any other programs that could block avast from updating properly. like a third party firewall?
i so make sure avast have access to the internet throw that firewall.
this is what i can give as a tip. hope this solves your problem if not write back.
and a happy new year i add to :).
i have Ashampoo FireWall FREE
Get rid of it…!!! Ashampoo doesn’t work with avast.
asyn
what FireWalls work with avast :
Comodo
Online Armour
Outpost Firewall Free
etc…
Please make sure you get a complete Unistall so as no remnants of Ashampoo are left on your system before installing another Firewall. 
Check this out:http://www.ashampoo.com/en/usd/sde/0050/2317/Ashampoo-FireWall-FREE/Ashampoo-Firewall-Free-hasn-t-been-removed-completely
Do not use Comodo:
[b]Melih Abdulhayoğlu: genius, madman, or just purporting another cloud scanner? [b]
http://forum.avast.com/index.php?topic=68145.0
@YoKenny
I don’t see the point of posting the link of Melih’s topic all over the forum… Chill out, OK?
Back to topic… I recommend the use of Online Armor. But that depends on your personal needs (of course) so good luck with the choice.