Apple tv hdmi says check device power

Is the Apple TV box status light glowing continuously? It should, else the TV won’t detect a device stream.

Have you tried using the Siri Remote to wake the Apple TV box? Or does the TV normally turn on the Apple TV box?

Also, please review: If your Apple TV isn't working, won't turn on, or shows a black screen - Apple Support

The light is glowing continuously. I think box is awake.

Alright. ✓ That part is working.

It airplays audio but no video. It still shows turn on, but audio airplay is connecting?

Is this AirPlay to an Apple TV 4K model? Older legacy models (not AirPlay 2-compatible) may not support AirPlay streams from some content providers. Any model may not be able to receive video streams from other content providers that block AirPlay altogether (e.g. Netflix). Some (web) video may not be formatted to be compatible with AirPlay.

Identify your Apple TV model - Apple Support

Find your Apple TV model number - Apple Support

What content are you trying to stream using AirPlay?

If screen mirroring or streaming isn't working on your AirPlay-compatible device - Apple Support

Additionally, you may get a black screen if the video settings are off (e.g. configured for a different TV), like resolution or dynamic range. You may use the remote to cycle through various video settings to find a compatible/​working video setting: If your Apple TV isn't working, won't turn on, or shows a black screen - Apple Support.