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.