Can't see menu on Denon 5308

You may have inadvertently turned off the video output you use. The front panel buttons may include one for "audio only" (which shuts off ALL video inside the component) (I have this feature on a couple of devices)
Or, you may have made the video output 'digital only' or some other thing. (I have a Denon 4806 receiver, and have to say the menu is the most primitive display possible. Kind of MS-DOS in a Vista world.)
Try using some of the other types of video outputs and maybe one of them has your menu still output via it.

Some need to be told if they are outputting menu to a Progressive signal, as RW said hook up a simple composite video cable to get menu up and verify settings.

Most menu systems are output thru the S-Video or Composite connections. Double-check those connections, especially if you're using the S-Video - they're notorious for backing out a bit and breaking the connection...

-RW-