Problem with Denon 2802 remote

The remote (RC-903) for my Denon 2802 is not working correctly. Pressing the Off button turns the unit off, and volume can be controlled from the remote. But pressing the On button does not turn the unit on, although the red light on the remote blinks when the On button is pressed. Likewise, pressing the input source (e.g., DVD, VDP,etc.) buttons on the remote does not change the input source on the receiver.

Batteries are new, and I've tried using the remote within 1 ft of the receiver.

Does anyone know what might be causing this problem? Thanks in advance.

There is no Main zone setting on my remote. I reset the microprocessor following the instructions in my owner's manual...unfortunately, that did not correct the problem with the remote. I appreciate the suggestions, though. Any other ideas? Thanks.

No, we have not added any new devices. There is a lot of light in our room, but the receiver has been in the same spot for 10 years, and this problem just started occurring. And, if I'm understanding your point, the problem occurs both in the daytime and at night. Thanks.