The entire TV screen is blue and there's no picture
The issue where the TV displays a blue screen with no picture most commonly occurs with older systems where you're TV is connected to a set-top box or a VCR using a coaxial cable and it's required to set your TV to channel 3 or 4 to receive the signal.
If you're using a device that needs to be set to channel 3 or 4 to receive a signal, confirm that the device and TV are set to the appropriate channels. If you're using a VCR that is turned on, but not playing a tape and not tuned to a receivable channel, then a blue screen will display on the TV. To resolve this, turn off the VCR or tune it to a receivable channel. If a cable or satellite set-top box is connected to the VCR using a coaxial cable, then the VCR should normally be set to channel 3 or 4 to receive the signal.
Additional troubleshooting is available if the TV has no picture, no power, or the LED light blinks/flashes red.