I have XBMC running on a win 7 machine and I can't get it to totally fill the screen. There is always, on all media files, black bars on all four sides.
any idea what I can try?
It sounds like you have the device set to "center" images and keep aspect ratio. You probably want to look into setting it to "stretch/zoom" to fill screen.
I know this is old but I stumbled across this and in case no-one else can research shortcuts (from here):
on your keyboard (PC), Z Zooms/sets aspect ratio
or while watching a movie click the Video Reel icon and click view until you find what you want