Thanks, sorry for my ignorance but the coax that went from the ONT to the router has been disconnected for a few days already and tv picture is fine. Does that mean that there's a separate coax that is connected to the ONT that is supplying picture to the STBs and that just a splitter in the living room would be sufficient?
Are you sure there isn't coax connected to the ONT anymore? The coax provides RF to the STBs for video. The coax going to the router creates a MoCA network for the STBs for the Guide/On Demand.
Just take the coax out of the STB in the Living room, connect it to a 2 port splitter one will connect to the router and the other will connect to the STB. Reboot your STBs and your Guide will come back.