I don't know if this is related but when I switched from a CRT to a ViewSonic LCD panel, all of my videos (avi, mpeg, whatever) went dark. I searched the web and found a lot of nothing. I went back to my monitor setup files and ran the setup wizard. I ran it in advanced mode and it had a place to set the color/hue/tone/brightness/gamma specifically for VIDEOS!! I made tweaks until their sample pictures looked right. Now, all my vids look normal again.
Hope this helps.