It won’t harm in anyway your system:
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, can you uninstall / boot / install / boot again?
The Vlk’s email is on the icon bellow his name (the envelope): vlk (at) avast.com