You would usually get a black or blank screen when nothing is connected to the input you choose. Most TV's would have a pop up stating so. If I remove the antenna cable from the TV, I get a black screen with pop up 'no signal' The DISH receiver is always in standby mode when not being used. You would get the DISH screen 'your receiver is turned off'. If the HDMI cable is removed from HDMI1, yo wouls get a black screen 'no signal'.
Did someone press the input button to a source that isn't being used? Is the receiver getting power?