Is there any errors/information I know you said it didn't give any ?
There may be something here - Check the avast! Log Viewer (right click the avast icon), Error, Warning, Notice or Info sections.
What is your firewall ?
Does it allow avast.setup internet access ?
- If it does delete the entries for them and do a manual update, this will force the firewall to ask permission again, allow it and check, remember, etc.