My mother has a Sharp LC-37SB24U connected to a cable box with an HDMI cable. She has no other components. The cable company programmed the remote to turn the TV on and off and control the volume of the TV. Now the problem. She cannot use the remote to change channels on the cable box except when she first powers on the TV. She then has like 15 seconds to change channels. The remote controls the volume of the TV fine and powers the TV off and on correctly. Could this be a problem with the HDMI handshake between the TV and the cable box?