Many Thanks for your replies Lyndel - I really wasn't expecting any!
The white screen I speak of only appears when I hold down the reset button, and then only briefly. I also I see a couple of vertical lines. If I don't hold down the reset button the screen uniformly and momentarily lights dark grey with faint "tick tick" repeating every few seconds. I've never seen anything resembling buttons/text etc
I've no idea on how to do a firmware update - perhaps you could give me a clue?