What is the best and free anti-virus software or website to

[Qarlcom]

I have this antivirus pro live thing i never downloaded that keeps popping up saying my computer is infested and it doesn't let me run any programs besides firefox saying they're infested, it wont let me run combofix avast or anything. The computer also won't go into safe mode every time i try to go into safe mode the text for files or directories or something comes up and then the computer restarts and if try to go into safe mode it won't let me. On top of everything else everytime i change pages on firefox like anything if the page has to refresh or I go to youtube or google or ANYTHING a new firefox window opens up with 2 blank tabs and the second tab has this in the address bar "http://™hÂŒ¬ÂÙûzx×kô�ûîòÄß]sjЇe§/;%14… WHATS WRONG WITH THE COMPUTER AND HOW DO I GET RID OF IT?! HELP PLEEASE PS.-malaware bytes doesnt work i install it but then it won't let me run it saying mbam.exe is infested I CANT RUN PROGRAMS, i can install malwarebytes but it won't run unlock iphone 3g
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