Any program I download, mp3 zip, from blog etc not related to MS Office ...
What happens if you submit these files to VirusTotal? Are they infected?
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).
If this does not help, can you uninstall / boot / install / boot again?