Windows defender turned off avast

For some reason my windows defender has turned on and i can’t turn it back off. Avast can’t be turned on unless windows defender is turned off so my question is what do i do to get avast back?

  • Which Avast…? (Free/Pro/IS/Premier)
  • Which version…?
  • OS…? (32/64 Bit…? - which SP/Build…?)
  • Other security related software installed…?