What Avast Product (Avast Free, Avast Premium, etc.) and version number are you using ?
What other security software do you have installed ?
How long has this been happening, what change around that time ?
Can you post a screenshot of avast supposedly blocking everything.
How do you connect to the internet, WiFi, Router or other ?
What is your Firewall setting Trusted/Private connection, otherwise it could block outside Public untrusted connections ?