L322 vouge 2003 radio

I haven't had sounds for over a year and was perusing some old threads trying to see what could be the problem. Trouble is that I'm an electrical numpty and although I've just renewed every brake pipe and mechanically service it myself I'm hopeless on electrics.
The left hand button at the bottom of the screen now does nothing for radio display, but the TV works but without sound. The parking sensors do sound. I'm not sure where the radio module is to check the fuse on top of it although I have checked all the fuses in the main pack. I have heard the term DSP but do not know what it stands for. I have checked the connections to the sound amplifier and they all look corrosion free. There doesn't appear to have been the usual water ingress to the boot area. She's a diesel if that makes a difference.

Any help gratefully received!

Hi again, can anyone point me in the right direction to find the radio module?
I believe there is a fuse on top of it that I have yet to check out.
I'm on night shifts at the moment so replies are as and when but thanks for any input.

7 years too late, rear load area lh compartment, the audio unit is mounted beside the av unit. Access to the bm54 is easier if you remove the black plastic moulding that becomes visible when you raise the spare wheel compartment cover.
hope you found it in the end.