I have had the same problems... I have to hook up component or composit and re-run the output config (reconfigure for HDMI, 720p, widescreen, and 5.1 output)
This just appears to be one of several problems with the 750 that will likely never be corrected...
My advice would be to not buy another Dlink media player in the future, as their lack of support with this 750 since I bought it has soured my opinion of D-Link