Thanks guys for your very quick response. Anyway I found out what the problem was. I guess there is some kind of control switch somewhere (may be related to the clips on each side of the display unit) which prevents the display unit to work until it fits perfectly under the radio unit. I had to press on the display unit pretty hard before hearing the click of the clips. As soon as I heard the click the display started working again. The reason I removed the radio and display unit this time was to hide the wire of my new GPS unit which sits now on the dashboard over air vent.