I've used the Belkin AV360 HDMI to MDP adapter to use my iMac as xbox display. Some weeks ago the adpater suddenly stopped working so that neither xbox or mac detect each other. I checked all the cables, they are working.
The adapter does not have any lights etc. to find out its state, so I don't really know if it's broken or if it's an OS X software problem (e.g. due to some update). I'm running OS X 10.8.2 (12C60).
Any clues how to proceed are very welcome!