The most probable reason is that you haven't formatted your Playstation 3 to your television. When you turn on the Playstation hold down the power button for about 10 seconds.
The first thing to do is make sure your TV supports the resolution you are outputting. If you have an older television, sometimes the hdmi connection will not work with newer electronics.
First verify that the TV is on the correct input channel. If it is, try using different video output options, odds are it has the wrong video output settings.
Make sure the cable is inserted properly and check if you have selected from the Settings menu of the PS3 video output HDMI. If the problem persists use another HDMI cable.
Well the first thing to do is reset the video settings if you didn't change them earlier. Turn the tv on and then switch the ps3 on and hold the power button. It should beep to let you know the setting changed.
