How to extract a Sat Nav screen on my Peugeot 807?

Just had the screen go black on my 05 Peugeot 807. Radio/CD still are operating, however radio goes off after 5 mins or so and the Emergency call button starts flashing ???? Checked fuses and all ok. Want to check the power to the screen but have no idea how to extract it out of the dash. Any ideas on how to do this + any ideas what else could be wrong ?