I have just installed the 400F on my system and when I try to do a flight, it loads up fine but after a minute or 2 all the sceens on the panel go blank and no matter what I do I cant get them to come up again. The FMC still works and all the switches etc seem to work fine. Anyone have any ideas?NH

Sounds like an activation problem. Try reinstalling and reactivating, if that doesn't work, contact PMDG support through email.