The most common reason for a TV to display a blue screen with no picture is because the source device has not been set to the proper mode.
If you are using a cable or satellite set-top box, ensure that it is turned on and set to an active station. If the set-top box is connected to the television using a coaxial cable, then the television should be set to Channel 3 or 4 to receive the signal.
If you have are using a VCR that is turned on, but not playing a tape and not tuned to a receivable channel, then a blue screen will be displayed 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.
If the blue screen is not because of a connected VCR or set-top box, the TV may require service.  Go to Product Repair.