help!!! "avast! firewall NDIS miniport #51"

Hello,
yesterday I received a pop up alert messagge stating that a driver (avast! firewall miniport #51) was not successfully installed.
I never tried to install any driver (it seems it was doing by itself) and since that message came out, no more connection to the modem/router was possible.
I have w7 and avast internet security (full paid version).
I do not not if it is important but it happened after last windows update.
I tried to start in SAFE MODE but still the same message.

Repair avast!:

  1. Control Panel → Add/Remove programs → avast!
  2. Click on ‘Repair’.
  3. Follow instructions.
  4. Reboot.