Invalid format on appleTV

OK, try another HDMI cable to begin with, if this doesn't help...

Try the following steps for the Apple TV 2 & 3, check whether things are working after each step where appropriate, before trying the next.

1. Restart the Apple TV (Settings ➔ General ➔ Restart).
2. Restart the Apple TV by removing ALL the cables for 30 seconds.
3. Restart your router. (Also try removing its power cord for at least 30 seconds)
4. Reset the Apple TV (Settings ➔ General ➔ Reset ➔ Reset all settings)
5. Restore the Apple TV (Settings ➔ General ➔ Reset ➔ Restore)

You may be unable to perform the last steps if I understand your issue correctly, if so...

If your problem persists get yourself a micro USB cable for the Apple TV 2 and 3 models or a USB-C cable for the Apple TV 4 (sold separately), you can restore your Apple TV from iTunes:

1. Remove ALL cables from Apple TV. (if you don't you will not see Apple TV in the iTunes Source List)
2. Connect the micro USB (or USB-C) cable to the Apple TV and then to your computer.
3. Reconnect the power cable (omit this step for Apple TV 2)
4. Open iTunes.
5. Select your Apple TV in the Devices list (which can be found below the volume slider near the top of the iTunes window), and then click Restore.

(You may already have a micro USB cable if you have a camera or other digital device)

You cannot use this method with the Apple TV 4K and will need to take the unit to Apple if a simple disconnection of all cables for 30 seconds doesn’t address the situation for you.

Does it play other content from Netflix?

What is it you are trying to play?

For clarity, are you saying the Apple TV won't turn on properly, not that Netflix won't load.