Options:
- Get a copy of Malwarebytes Antimalware on a memory stick, boot into safe mode and copy it across to the local hard drive, then boot into safe mode with command prompt and execute it from there via the command line (note - a lot of recent viruses infect the windows explorer, and safe mode with command prompt is the ONLY mode of bootup which doesn't automatically load a copy of explorer.exe...in fact it only loads it if you do something explorer-y, so avoid that!)
- Rip out the hard drive, mount it as a slave drive in a separate working PC and do a scan from there. This is probably the quickest option, IF you have a separate working PC available. Note, ensure you have a virus scanner and MBAM on that separate PC *before* starting the exercise.
(this isn't an exhaustive list, but my 2 best shots at killing your issue in the most effective, quickest way).