When using HDMI cables for a PS3 games console, you should follow these instructions:
Switch on your LCD or plasma TV and set its input to the HDMI setting.
Use an HDMI cable to connect your PS3 to the LCD or plasma TV.
Switch on your PS3 and press for a few seconds until you hear the PS3 start to bleep and let go of the power button.
The PS3 should now configure itself for HDMI video and Audio output so long as the HDMI cable is properly connected.
If you need further assistance, Sony customer services are available to help. Alternatively, consult your PS3 manual.