I recently had an issue that may be the problem that is being described in this thread, but I am unsure so I will describe my issue and my solution.
I have a 2005 LR3 HSE, no installed bluetooth phone. I loaned the car to a friend and when it was returned the radio was having an issue. It would turn on, switch between accessories, but would not produce any sound. Turning the volume knob would not switch the display to show the volume level as it normally would, it just did nothing, yet the volume knob would work in settings modes that used the volume knob to make changes.
Reading the forums I found lots of information about upgrading the firmware in the radio, replacing the radio, checking the fuses, muting/un-muting the radio, disconnecting the battery to reset the computer. Nothing that really made sense, except perhaps the muting/un-muting thoughts, except there doesn't seem to be a way to mute or un-mute the radio.
On a fluke I was going through the tone settings in the radio... the place where you have base, treble, balance, fade, a few other things, including "Reset Tone Settings". So I decided to see what 'Reset Tone Setttings" did and, um, it fixed the issue. So somehow the radio was "muted" or something, and there wasn't an "un-mute" but resetting the tone settings resolved the issue. I don't understand it, but was happy to find a solution that didn't cost anything.