display fault on synergy 3505?

The bottom half of the display screen on my BT synergy 3505 is blank suddenly. I.E. You only get the top part of all characters across the display. Not aware of having dropped it but may have used with wet hands - could that have caused it?

Any ideas for fixing OR any advise on how to take apart - unscrewed the two small screws inside the battery compartment but the two parts do not then prise apart

Many thanks