Dash4 Pro screen blank

[robmug]

Dash 4 pro stopped working yesterday at Donington part way through the day with noting else going on.
RT Live was powered through the day; Dash 4 takes power from there.
LEDs to the side of the screen were working, so there was still power to the Dash4.
We tried disconnecting/reconnecting
We tried turning RTLive off for 10 mins and powering back on.
Did we miss anything?
Any suggestions?
(we're back on track at Oulton on Saturday and ideally would like it running by then)