Basically I have the same problem that has been displayed a lot on this site. My pioneer DEH-P7800MP display won't show when the face closes. When the face opens up all the buttons and lights and display work but as soon as the deck closes everythin doesn't work...I've read a lot of blogs on here with the similar problem and no answers on any. Those posts were about a year old so maybe now there are solutions. Is it the ribbon? Man idk and I went to 2 audio places and both guys didn't know how to fix except tellin me to buy a whole new deck.

The faceplate and head unit is is attached via a flat ribbon cable. (Caution only continue if you have some courage). If you open the faceplate you will see that the ribbon cable is seated in too a flat connector on the PCB (Printed Circuit Board). This connector has a locking mechanism on it that when locked presses the contacts of the cable to the connector. Ensure that the cable is seated properly and that the latch or the lock is in the locked position. Assuming that the tension lessons when the unit is closed so it draws away from the connector and when the unit is open it pulls tension creating a contact. If you see no signs of mishap on this end of the connector try the other end.
Hope this helps.

Assuming the flat ribbon that connects the faceplate to the PCB is seated correctly at both ends you probably have a break in the ribbon where it bends upon opening and closing the faceplate , you can buy a new replacement ribbon from Pioneer for about 26 dollars part number - XNP7026 faceplate ribbon cable.