First off, don't panic. However spooky it looks, this particular 'nasty 'is not actually that nasty. All it's trying to get you to do is pay out some money for a 'cure' to a disease your PC doesn't have, and you're not going to, so that's that. It's
not a real virus/trojan. They can do genuinely nasty things.
So, next thing is to get rid of the annoying popups. Malwarebytes is good, but it looks like Antivir is being clever enough to prevent you getting it. I would suggest that you try downloading
spybot. If that doesn't get rid of it, and/or Antivir stops you downloading it, as HJ says, try downloading Firefox or Opera, then download Malwarebytes/Spybot.
But like I say, don't be spooked - this is a nuisance, not a pooter-killer.