Video output problem on PS3?

my ps3 was connected to a HDTV using a HDMI cable. Now I no longer have the HDTV and I don't have a HDMI port on my old TV. I only have yellow/white/red ports. I connect the PS3 to them using the AV cable and I can hear the PS3 booting, I can hear when I'm moving through menus but the screen is black. I tried pressing the power button until I hear the second beep but nothing happens. It is booting normally and I can hear the starting sound. What can I do? the cable is ok, the PS3 is ok