Normally you just use the TV remote to switch inputs. I don’t know what “TV” means and what “no TV means” – for example is there some kind of error message and does “TV” mean any kind of video or something specific like Dish network TV. Is the Roku attached via HDMI2? If so, after switching to HDMI2, did you try pressing the Home button? – just incase the Roku had gone to sleep.
By the way, I have Dish and Roku, and there is nothing special about Dish in terms of how it interfaces with your TV. In my case, Dish is on HDMI1, and Roku is on HDMI4. If I have the power saving feature on my Roku enabled (as it was by default), then after selecting HDMI4, I press the Roku Home button to wake it up. If I turn the Roku power saving feature off, then as soon as I select HDMI4, I see the Roku screen saver.
Oh and if you were switching your TV back to Dish, but it was switching right back to Roku, then go to settings->system->Control Other Devices (CEC)->1-touch play, and try disabling that. That sometimes works “much too well” and grabs the TV’s attention when it shouldn’t.
