However there would be a first time for everything. I always carry a spare shiny new HDMI cable but HDMI HDCP handshakes (see the web please) can cause this. So we always try another source when we've swapped TV and cables.

In the past we could sidestep HDCP handshake issues by connecting over Component but those days are gone.

Be sure to have power downed, removed power from ALL HDMI DEVICES when swapping in gear. The HDCP gremlins are alive and well.
Bob