Blank Video Screen
The video settings for your PS3 when connected to an HDTV are not compatible with your standard-definition television. When you switch over from HDMI cable to composite cable, your screen will remain blank even though the console is on. The AV cable for the PS3 connects to a different port than the HDMI cable. When you change to the AV cable without first switching your settings, your PS3 still thinks you're connected to the HDTV using the HDMI cable.
Resetting PS3 Video
If you're already on your standard-definition television, you can reset the video settings using the power button. Turn off your system first, then press and hold the power button for five seconds until you hear a beep. This will cause the video settings to reset to their default, which will work with your standard television. You can further modify the video settings as needed from there.
Choosing Video Settings
Go to Settings, Display Settings and Video Output Settings in the PS3 menu to change your video settings. The PS3 has four video output options: HDMI, Component, Composite and AV Multi/SCART. The Composite setting is what's compatible with the PlayStation 3's AV cable. This displays video at 480i, and greatly limits other options for resolution and screen ratio. Follow video setup prompts and save your new settings.
Avoiding Future Errors
If you make frequent switches between televisions ̵1; such as moving the PlayStation between different rooms or taking it over to a friend's house ̵1; the easiest way to avoid this problem in the future is to manually change the video settings before disconnecting the console from your HDTV. HDTVs can display the lower resolution settings required for standard televisions, so this doesn't result in the same error when you go from standard definition to HDTV.