A couple of other things to check:
HDMI connector - is it fully seated? Both ends? No sideways play in the connector?
Really long HDMI cable? Boosting it a bit more might help. Try 7 and work down from there.
Does it boot up with composite output even though the HDMI cable is inserted?
I would suspect the cables/connectors first, but try: (from http://elinux.org/RPi_config.txt
Unfortunately, it doesn't have a list of other bits to set/clear for other fine(!), oriental displays.
You are in a maze of twisty little passages, all alike.
When General Failure and Major Disaster get together, Private Parts usually suffers.