Ransomware messed up my latop please help

Hi
Was browsing innocently today and up came a pop up saying I was infected with goodness knows how many trojans. Then I clicked on something (lethal) and it said did I want to pay an amount to have these things removed. I didnt want to pay and cliked out but pop up after pop up happened an updater appeared in my windows defender program. That seems to have installed now on my pc but is coming up as a threat along with sa7236.3exe when I ran a trial of prevx.
I have run panda, super antispyware, adware, spybot and a-squared. All didnt detect these two things but prevx still is. At first my task manager was lost but that came back when I ran combofix.
can anyone help please. I assume I am still infected and I believe this is a severe security issue. Dont want to have to reinstall windows but it looks like I might have to. Also just ran HJT but it kept saying something about host files and not working properly though in the scan I did see at least 1 no name button that I couldn't delete. Pleeeeze can anyone help me? thanks so much

 

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