I will bet it's the connector that goes into the control module, it's located on the drivers side footwell, it's a silver box, the wire that goes to it that supplies power is black/yellow, this is where the problem will be I'm sure. You've probably inadvertantly knocked it when getting in/out the car and it's working again. The fuse that supplies power to this is number 22, BUT this also does most of the dash as well as the low fuel/washer level lights etc beside the clock... so it's unlikely to be that if they are working and the display is not. Obviously there is a possibility that the display is faulty but there are no moving parts and unlikely just to stop working all together. My bet is defo the connector that plugs into the module, look there if it dies again.