Hook up your PS3 to you 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. And that's it. You should be set. If not, then the TV is acting rather strange.
EDITOR NOTE - If this still does not work, make certain your TV is on the correct HDMI input! -