Unplug all HDMI (i unplug just one end from each cable) then remove power from each HDMI device for about 10 minutes to get the HDMI chips to reset. Now connect up again, be sure you are on the HDMI ARC port of the TV (many Samsung use port 2, but check documentation.)
Power up and re-test. If it fails you need to test this bar on another ARC source.
We have been using a Samsung HW-HM45 sound bar with our 55" Samsung LED tv for about a year with no problems- until Saturday, when the power went out while they were on- when the power came back on, we couldn't get any sound from the sound bar- we have tried everything (including calling Samsung) and can't get it resolved- it will show "D.IN" but will not switch to "TV ARC" to give us sound- my question is- is the thing fried or is there something else I should try?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic