1. You can desinstall avast, boot, install again.
    or
  2. Be sure that the following links are in your startup registry keys (or, at least, at your startup folder):
    C:<avast folder>\ashmaisv.exe
    C:<avast folder>\ashDisp.exe

You must have two services running in automactically mode:
avast! Antivirus - Manages and implements avast! antivirus services for this computer. This includes the resident protection, the virus chest and the scheduler.
and
avast! iAVS4 Control Service - Provides automatic updating for the avast! antivirus.

I hope this help… :wink: