The computer screen on my Vauxhall Astra Trwin top goes blank intermittentl?

The screen inside of the car showing radio,phone,satnav keeps going blank. The central locking does not always work either . Are these 2 components connected? When the screen is blank, I can still access the radio and phone but the sat nav disappears. The garage has told me there is nothing wrong with the car but it is driving me mad!

Wendy
October 2009