What's causing my stereo to not work and my clock to stop while I drive?

a few days ago my car stereo kept cutting out and coming back on again intermittently, then started making buzzing noises. Then it stopped responding to the volume control on the steering column. Now the stereo has turned itself off completely but occasionally switches itself back on briefly though no sound comes out before it goes off again.

Also, since the stereo has turned itself off more or less permanently, the clock on the display (where the radio station usually shows) stops at the time I set off on a journey, but does continue to flash the seconds. Next time I get in my car the clock is right again but stops again while ever I'm driving.

I have checked the wires and they all look ok.

Can anybody shed any light on this? It is a Citroen C3 with factory fitted Clarion stereo.