If you are using HDMI 2 on your TV and you get an image from your cable box, then you should be good to go for connectivity to the TV from your Blu-ray Disc (BD) player.
If you are using a UHD BD player, then you likely will need to bypass the A/V receiver to get video to the TV on a different input of the TV. Assuming it is NOT a UHD BD player, but a standard BD player.
If the receiver shows cable just fine when the TV is on HDMI 2, and your receiver is on cable, then switch your receiver to the DVD input. If the image goes away and you get no image from the BD player, then swap the cable on the back of the receiver with the cable box. Yes, swap your BD and cable connections.
Your cable box is now on the DVD input. You know the cable box works, so you should see an image. Now switch your Denon back to the cable input. Do you see an image from the BD player? If so, then your Denon needs to have the proper HDMI input assigned to the back connections.
This is all in the setup manual for the Denon. Basically, it allows you to assign the various HDMI connections on the back to whatever you would like them to be. This can be confusing if they aren't set to match the labels that are already on the receiver, but it is important to ensure everything lines up properly.