Did you see a splash screen for the Apple TV?
If not then the "no signal' message is the TV not the Apple TV.
Assuming that the Apple TV is powered up and will at least show some kind of display
1. Try a different HDMI input.
2. Try a different HDMI cable.
3. Try a different source to make sure that the HDMI input on the TV works.
3. If the Apple TV has been used on a different TV before this the output may be set to 1080p which your TV may not be able to handle. Connect it to a different newer TV and see if you get a picture. Change the output to 720p. Try it on the Polaroid now.
If you don't get anything then Apple TV itself may be bad.