My car radio (a Renault OEM model made by Blaupunkt) is playing up...
as soon as I switch on, it beeps loudly about once every 5 seconds.

Now, I've had this for years, and recognise this noise as being the
same as the radio makes whenever it gets disconnected from the car
battery - ie when it activates its code protection and wants a PIN
entering to switch off the whining.  However, in that instance, the
display flashes "CODE" while you enter the digits, and without that,
you can't input the code.

So, I thought, - I know, if I actually unplug the radio it will switch
into 'code input' mode and all will be well.  Clever, huh?
Unfortunately not: despite unplugging it for the whole day, when I
plugged it in again, there was still no 'code' display, and STILL the
bleating.

So, is the radio totally stuffed?

Thanks
David