Thanks everyone.
A friend must have set the brightness to minimum while looking at some pics from his camera, assumed he had switched it off.
On charge overnight & alarm went off following morning to get plane, display was OK as it was still on mains power.
Even so I should have realised having used the Zaurus ever since the first C760 came out.
Put it down to old age, retire in 3 months time, not long after the Zaurus range went into retirement.
Mike