I dont know if you resolved the problem or not. Just thought Id offer some advice. The PS3 will automatically detect an HDMI device and will adjust settings, but in my experience they have to be manually reset to accept the A/V cables. Never tried holding down the power button.
You may have to hook the PS3 up using the A/V (red, white, yellow) and the HDMI, go in and change the settings in the PS3 to use the A/V out (cant think of what it is called off the top of my head), then switch inputs on the TV to the A/V input. It should show up then. Accept settings and carry on.