I know it’s a long way, but just check this forum to be sure of your system would be scanned at DOS.

Norton mess, at least, three Registry keys…
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\VirtualDeviceDrivers
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet001\Control\VirtualDeviceDrivers
HKEY_LOCAL_MACHINE\SYSTEM\ControlSet002\Control\VirtualDeviceDrivers

You should also use RNAV2003 or this link to download and then remove traces of NAV into your registry: for removing the most fastidious at clearing out the vestiges of the software and sparing users’ headaches. Download and run the application. If you have already done the first step, choose ‘No’ to continue.

Good luck. :o