Does it work eventually if you leave it on? Onk 606's had failing HDMI boards. The problem usually first presented itself by HDMI handshakes taking a long time to connect (sometimes 5 minutes or more) and progressed to complete HDMI failure in many cases. The solution, I'm afraid, was to have the HDMI board replaced - a costly repair, unless you're still under warranty.
Hopefully, that's not the case with your 705. First thing I'd test is replacing the HDMI out cable.
Hopefully, that's not the case with your 705. First thing I'd test is replacing the HDMI out cable.