Same problem for me with latest SVNs :
For some files, the Normal mode (only in windows) doesn't work. other modes (zoom, original..) work fine.
No problems in fullscreen mode : all modes work !!!
Another solution find : put the original mode by default in the setup...
The problem I have with some videos is that in fullscreen, there is sound, but no picture, but if I backup to the playlist screen, the now playing preview works fine, but still no picture if I go back to full screen.
I try altering the zoom mode as suggested and see if that helps.
EDIT: All other modes for aspect ratio display properly except for the Normal one.
God this is annoying, as I can't work out why. I've analysed files that do & don't play with media gui, and I can't see any encoding differences between them to see what the problem is.
Thanks sray!
DPI settings was the problem for me to. I had the problem as most of us has. Black screen with sound first time after starting MP. I hope the development team can fix this problem now. DPI increasing is a must on my Sony 40" 1080P.