I am having a not disimilar problem. Having returned one WD HD TV Mini to Amazon because the HDMI port stopped working on 2nd day, I have received a replacement and the HDMI doesn’t work again. My 47" Philips Plasma 1080p TV simply shows “unsupported video format” when connected to the WD HD via HDMI. Doesn’t matter what TV parameters I change (even did a software update for my TV) it WILL NOT work.
Composite works fine, but of course simply does not playback, nor display HD home videos, or large format (digital camera) photos. Have heard nothing from WD, so will have no choice but to return (yet again) this device. It’s a shame as it ticked-all-the-boxes and I mostly use WD HDD - but this is rubbish. Or a bad batch. I just don’t know. Anyone else having similar issues?