Did you switch from an HDMI Cable to RCA Cables by any chance?
If so, just simply press and hold down the Power Button of your PS3 while it is in Standby Mode (Red Power Light) until you hear two beeps. This should restore your picture.
You can take the help of expert technicians who will help you to fix your hardware device and any problem connected to it. So kindly go for a technician from your nearby area and get your problem solved from him.