I started with P3Dv4.4 a year ago last December.  Got all my addons installed and everything has just been great.  I was using Win 10 and Foxfire.  A couple of months ago I started having problems with P3D and discovered there were updates to P3D.  I update everything else, but didn't have a clue P3D had to be updated.  I discovered this P3D update requirement when I started opening P3D and if I clicked on the Options button, P3D would CTD.  I installed the latest Client plus and now am up to date and everything has been running fine.  A month ago, I just got overloaded with Foxfire and Dashlane password manager, and let my IT guy install Google Chrome.  Everything has been going pretty well with P3D, but I soon discovered that Chrome would not open until I shut down Win 10 Anti virus.  I could turn it back on with no problem after Chrome was open.  Also, I have in general shut down my Anti virus (including everything for P3D excluded from anti virus scans), while flying my flight sim.  Today, I was setting up a cross country and went to open P3D, and nothing happens.  It doesn't even blink.  It's just in in-active.  

So, any comments about why this has happened will be appreciated,

Mike Nicholson, Jetline Systems PC, 4.20 Intel 4 Core i7-7700k CDU, Nividia GTX 1060 6GB card,  32722 mbs memory, Windows 10- 64bit, Prepar3D v4.4

The first thing P3D/FSX does when starting up is to load the modules in the dll.xml.  In P3Dv4, there are two dll.xmls.  One in same folder as P3D.cfg and one in same folder as scenery.cfg (new default).

Just a thought.....are you running Prepar3D with Admin rights, a lot of windows programs do funny things if this isn't set

Mine got stuck a few days ago and I couldn't start p3d up. Task manager showed p3d using about 2% CPU, and it would never start. I fixed by editing the prepar3d.cfg file and changing the start up scenario to a different one with a default aircraft.