We will need more information to be able to help you:
- Which OS are you using? Is it up to date?
- Do you use a firewall? Which one?
- Do you have any other antivirus installed in your system?
- Any other security programs that could interfere?
Which is your Windows? 98, Me, XP?
Do you use any other antivirus in your computer?
Can you try to repair your installation?
Go to Control Panel > Add/Remove programs > avast! antivirus > Remove. Then choose Repair function in the popup window (Repair). You must be connected to the internet while repairing.
If this does not help, I suggest an installation from the scratch:
- Uninstall avast from Control Panel first.
- Boot.
- Use Avast Uninstall for complete uninstallation.
- Boot.
- Install again the last version.
- Boot.
- Check and post the results.