Sometimes PS3 consoles, when connected with an HDMI cable to the TV to play video games, display a Mode not supported message. This FAQ will show you
Fix Error When Connecting PS3 with HDMI Cable
Hook up your PS3 to your TV with the HDMI cable. Now, when you turn on your PS3, hold the power button on the PS3 for 5 seconds.
It will reset the PS3 video options and recognize the HDMI connection. It will then search for the correct resolution settings on the TV. Press X to confirm.