Casio CZ/ VZ/ FZ - Pro Series

Hello there - I recently picked up a cz-101 at a car boot sale with
which I'm having some problems with. Basically, it won't start up. All
the lights come on for a split second then all the pixels on the
screen come on until i switch it off. Sometimes, (or, i have
discovered, always if i hold down the ring-modulation button while
switching it on) it manages to boot and for a tantalising approx. 2
seconds max I can get sounds out of it. As far as I can tell, all the
correct voltages are being supplied to the main board, I've tried it
with batteries and ac/dc adaptor, and frankly i'm a bit stuck.

Do you reckon you could throw any light on this conundrum? Any ideas
would be gratefully recieved.

Thanks,

David