I recommend installing Malwarebytes's Antimalware.
Not only is it free, it worked better than Norton ever did. Takes a few hours to run, though, but the results are worth the wait. Completely removed the program "Anti-virus 2010", which did something very similar to yours; it completely ruined Windows Defender and Norton.
If it won't let you install it, try using a USB to copy the installer onto the computer, then see if it can run it.