Hi, If the function included in the design, Try Shift-E, to open and close doors., Welcome to the Simms world Bob.*
Good advice Bob, but just to ellaborate a little, to try and open doors other than the main exit, try Shift-E like Bob said, but immediately after pressing Shift-E, press any # 1-4
Scratch built PC: 2.8G P4HT, 250G 7200RPM Hard drive, 1024 RAM ,GForce FX 5200 128, TrackIR3 Pro with Vector 6DOF Expansion Vo
Also since Shift+E then 1-4 is sometimes hard to key in exactly so FS2004 recognizes it some developers have mapped exits to other common animation keys like the Tailhook command ect. I'd give those a try too. Remember some of these aren't mapped by default. You may have to assign keys to them before they work.
In Memory of John Consterdine (FS Tipster)1962-2003
When you download an aircraft file the developer will usually add a read me file or spec sheet that will give you all the animation commands. But don't expect the same animations on different aircraft, not all engine covers open and sometimes the nose will open but the rear won't (the Anatolov 225 is a perfect example of this) and don't worry if the command for something is completely different then it's intended purpose (tailhook for refueler extension etc...) The basic commands for opening something by MS default is shift+e and for more than one door it would be Shift+e+2 Shift+e+3 Shift+e+4 etc... Happy flights and many great returns on the new hobby (addiction)
I don't have a C5 model but I had the same problem with both Antonov's 124 and 225 (similar to the Galaxy). It may well be 'shif+E, 2' but on mine the engines had to be turned OFF before it would open as well.