cazalea[Seiko Moderator]
20873
Don't fear
It could be something simple, like happened to my pal Moki and his Tudor:
A screw fell out and wedged into the stem area, stopping the rotor and the ability to set the watch

Notice the empty hole

Screw and clip back in place, tighten, and soon all is well.
Your watch may vary but this something I have seen a few times.
Cazalea