Have you tried the other HDMI outputs like 720. By the way there is no changing, the composite output is on at the same time as the HDMI, its simply whether your TV connects to the player correctly using HDMI. Try another lead or another HDMI input. What TV do you have.
Many older display devices do not meet the criteria (HDMI handshake) necessary for the Hub to be able to output to them via HDMI. This is a result of the HDMI anti-piracy requirements of content providers that were finalized after the manufacture of early HDTVs. Some units have the ability to upgrade their firmware, most do not. The only fix is to replace your HDTV with a newer unit or be satisfied with using the component or composite outputs from the Live Hub.