Komplete Kontrol instrument scan restart issue

So the system does a full reboot? Sounds like a bit of a major issue with a plugin by the sound of it.

Can you note what the instrument is that is being scanned when it crashes? Ideally if you have an idea which instrument is causing the issue you can just remove that 1 instrument but otherwise it's a longer process to test.

Do you have any other VSTs installed other than NI instruments?

Did you manage to launch KK at all initially and set any additional paths in KK to scan?

Basically what i'd do in this case is first just rename your VST3 folder so it does not get scanned. The VST3 folder is located at: C:\Program Files\Common Files\VST3

Rename this to something like C:\Program Files\Common Files\VST3-backup

Launch KK again and see if it loads. If it does, you have an issue in your VST3 folder. Add back a few plugins at a time and relaunch KK letting it scan the plugins. Keep doing that and if you hit the issue again that should identify the plugin.

If not and you have the same issue, possibly the issue is in another folder being scanned which without being able to get into the preferences would be difficult to see what is being scanned but you should be able to check where Native Access is installing the VST2 plugins and repeat the same process there