I hope some Linux users can help you here. Use a linux live cd, i think ubuntu live cd should do the trick, but wait for more advanced linux users as I am a Linoob as of now. I would recommend that if you backup all important data in the OS drive to other drives first. Format the OS drive and install any distro of linux like Ubuntu. Now clean your PC manually if you know which files are the viruses.
Otherwise, try EASEUS Partition Master Home Edition (its free) or Paragon Partition Manager(which is free for today only), if you have data in your OS drive. If not, then simply format again, reinstall OS, and use any AV burned in a CD (Of course son't burn a cd on your pc, burn on a virus free one) to install the AV. Once you have done this, make sure you update it (dl updates and then burn them to the same cd before you format). Update the AV from the cd itself. Don't connect to the net at all. Scan the whole PC and see if you can delete the viruses.