Firewall suddenly turned off

I use my notebook for working as well as playing legaly acquired games. I have played dota 2 then I switched out of game and then I saw firewall was down. Can someone tell me if it is probably a failure or an attack?

Repair Avast:

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