There's usually some type of handshaking between the two devices so make sure you follow the correct procedures for connecting them:
Turn off the power to the HDTV and HDTV Set-Top Box.
2. Connect a HDMI cable to the HDMI output of your HDTV Set-Top Box and the other end to
the HDMI Input (white color area) at the rear of the HDTV.
3. Turn on the power to the HDTV and HDTV Set-Top Box.
4. Select HDMI using the INPUT button on the remote or side of the HDTV, or directly by
pressing the HDMI button on the Remote Control.