HDMI not working on WD TV Live Hub

It sounds like you have taken all the correct steps to try to solve the problem. However, composite video is the “lowest common denominator” and if that does not work, you probably have a bad box. Also, the fact that you cannot manually change the video settings, and the fact that it worked for a long time and then suddenly failed, reinforces the idea that there is a hardware failure in the box. Unfortunately, it does look like you will have to buy something else.