You switch to the HDMI input expecting the Google TV home screen, and you get nothing. Black screen, or the TV flashes "No Signal" like the device is not even plugged in. The Google TV Streamer is small and it sips power, and that second part is behind a surprising number of these blackouts. Here is how to get a picture back, ordered from the fix that works most often down to the one you will rarely need.
Start with power, because that is usually it
The Streamer ships with a wall adapter rated 5V/1.5A for a reason. If you plugged it into your TV's USB port instead, that port often supplies only about 0.5A, and the device browns out: black screen, or a reboot loop where the logo appears and vanishes. This is the single most common cause. Plug the included adapter into a wall outlet, not the TV, and not a multi-port phone charger you are not sure about. If you have been running it off the TV's USB this whole time, that is almost certainly your problem.
Confirm the input, then reseat the cable
Make sure the TV is actually set to the HDMI input the Streamer is in. It sounds obvious, but auto-switching and CEC can leave you on the wrong source. Then push the HDMI connector firmly at both ends, and try a different HDMI port on the TV while you are there. A half-seated cable or a flaky port produces exactly this no-signal symptom.
Reboot the device
Unplug the Streamer's power cord, wait a full minute, and plug it back in. If you can still see the menu, Settings then System then Restart does the same thing. A reboot clears most temporary no-signal and handshake states, and it costs you thirty seconds.
Clear the HDMI handshake between TV and Streamer
If the screen is still black, power-cycle the whole chain. Unplug the Streamer, then unplug the TV from the wall and leave it off for at least a minute. Google suggests going as far as 30 minutes with every HDMI device removed to fully drain the handshake. Plug the TV back in first, then the Streamer. If you run the Streamer through a receiver or soundbar, plug it straight into the TV to test, since CEC handshakes get stuck most often in that middle box.
No light on the device at all? Isolate the hardware
If the small status light never comes on no matter what input you select, stop fiddling with the TV and test the Streamer itself. Try a different power cord and adapter, move to another wall outlet, and plug the Streamer into a second TV if you have one. If it stays completely dark on a known-good outlet, a known-good cord, and a known-good TV, the unit has failed. That is a warranty or replacement situation, not a settings problem.
Last resort: factory reset
If it powers on and shows a light but still will not output a usable picture, reset it. From the menu that is Settings, System, About, Factory reset, or you can use the button on the device per Google's instructions if you cannot see the screen. You will have to sign back in and reinstall your apps, so save this for after everything above has failed.
So how do you tell a broken Streamer from a broken setup? A Streamer that lights up and works on another TV points the finger at the original TV's input, the cable, or the power feeding it. A Streamer that stays dark on every outlet, cord, and TV you try is simply dead, and no amount of menu-diving will revive it.