Loose connections often cause the TV picture to tile or pixelate. Remove and reconnect the coaxial connections between your Set Top Box, TV equipment and wall connection. Make sure all connections are securely fastened. This is also a good time to inspect the coaxial cable for any obvious damage which could cause a loss in signal strength.
If this does not resolve the issue, you can call FiOS® Technical Support at 1.877.462.0488, 7 days a week, 365 days a year.