To force uninstall Norton Antivirus successfully, you need to make sure that the program has been fully closed, and all of its registry keys have been cleaned up. This sounds like a basic rule to uninstall any program, but none of these two things can be done easily, as Norton Antivirus embeds almost every part of its services into your system deeply, consequently making users difficult to either completely disable this software or locate every registry key.
First, to shut down Norton Antivirus, you can right-click the tray icon to close background services or killing its process by pressing Ctrl+Alt+Del to open task manager. But I think the safest place to force uninstall Norton Antivirus is in Safe Mode, which minimizes the chance to conduct wrong removals.
The second thing you need to do is to delete all Norton Antivirus files and clean up its registry keys. Normally going to Control Panel->Add/Remove programs can remove all major files as well as its relative registry, as long as you do it in Safe Mode. However, this can not give you a complete uninstall, you may still get Norton Antivirus services popping-up, and any attempts to re-install it or install other security software may be denied. If that is what happens in your case, you may as well try to find and locate and delete the files and directories.
Since the entries related to these files stay in separate parts of your registry and hard to pinpoint, you properly will risk a danger of messing up your registry while still ending up with a failing uninstall. I did not want this risk so I turned for a help when I wanted to force uninstall Norton Antivirus.
A small application named Best Uninstall Tool came as my final solution to force uninstall Norton Antivirus. It has a special method called Force Uninstall which can automatically look deep into your system and erase everything regarding the files and registry based on the directories and files you provide, meaning that you only need to locate the files mentioned above; the rest of the job will be quickly done by Best Uninstall Tool.