What is the exact model number of your Sony TV? Does the issue occurs when a different source device like a cable box, DVD player, gaming console, etc., is connected to the TV? If the issue occurs with different devices too, try changing the cable used to connect the TV to the source device. You may also try connecting the power cord from the TV to a different wall outlet.
If the issue is still not resolved, try resetting resetting the TV to the factory settings. Information regarding resetting the TV can be found in the supplied user manual.
If the issue is still not resolved, service may be required to resolve the issue. Refer to the following link to setup a repair for your Sony TV.