Infostealer.Consmiper and losing ground

I'm likely over-reacting as I'm not great with computers, but if you have advice, I'll take it.

 

Alright, so I am currently using Norton Antivirus and I did something rather stupid and have had a slippery slope since.

I recently used a youtube to MP3 converter and failed to realize exactly how dangerous that is for my computer. After a couple of days, I got the third ever Trojan I had seen appear on my computer. At first I thought nothing of it. The last two had died with relative ease, why wouldn't this one? Norton said it shot it down (Quarantined it), I sent a report in automatically and thought nothing of it. 

 

Well turns out my and my antivirus were wrong. Its still holding out. In fact, I got so worried, I did something even stupider trying to kill it. I downloaded Spy Hunter 4 to look for it. When it said I had 200 errors (the original 6 it said was stretching it) I looked up how sketchy it was and promptly blasted it.

However, the debacle took a casualty. Norton antivirus is down (Errors 8504,104. Norton is calling for an uninstall and re install, but that would let this Trojan run amok for about 20 minutes)and I pulled up Windows defender as fast as I could as a last stand. Consmiper comes back about every hour or so and launches an attack, and I don't know if Defender can handle it. I also don't know what Consmiper knows (If it can only track what I have logged into since it came, I'm safe. I have avoided Paypal like the plague during this).

Basically, my defenses, my one weapon (Power Eraser) and my emergency processing(Old Computer= Worn Out Ram= 10% out of the lag zone at this point) are all down. My last stand is a default antivirus defender that hasn't been updated or used in eight months. I might be overreacting (I hope I am), and its a minor thing, but I would love to know EXACTLY what to do.