I am a bit confused. Are you saying that your Windows system drive used to be D: before?
Or did you change the location of the Plex data folder already some time ago?
Either way, changing all references from D: to K: in the Registry should make it work again.
Make sure to follow the “Addendum” as well in here: [HowTo] An extended guide on how to move the Plex data folder on Windows
Once you have it running again, set the startup mode of the “Plex Updater service” to “Automatic delayed”. This will improve reliability of automatic updates.
