Honeywell ST7100 programmer goes blank when RUN selected?

10 minutes after I came home yesterday(28/12/2012) the power cut . Since then the central heating/hot water have not been working. I think the batteries are okay, because you can still get the display, However, as soon as you press RUN it doesn't click on and you lose the display. I have a Honeywell ST7100 programmer. Any help would be appreciated. PS, I changed the fuse at the switch but nothing. Help. Dannie