I have a similar problem with a new f6400 series.
If I unplug the tv for a bit then plug back in it seems to clear problem.
Exact model is UE40C600, approx 2 years old.
Just tonight, it re-booted, then again, and again....
I tried removing LAN as I heard it could be an issue, also the remote (remove batteries) and the damn thing keeps re-booting after after 5-7 seconds. It plays a re-boot chime then again and again...
Issue is I cant seem to get TV to remain on long enough to try system re-set in menu, as it re-boots.
I really cant afford a new TV and being a 50/50 dad with kids I am a bit at a loss
Any help truly appreciated