LG 37LH4000-ZA Problem?

Problem at switch on as can be seen with the lines across the sceen.Sometimes it take several seconds for picture to become stable or 20 minutes or more on other occasions. When the picture starts to appear it initially appears squashed into the top 1" of the screen. Keep an eye on the top of the picture which shows a similar effect after changing channels at which time the picture also freezes for 2 to 3 seconds. Approximately 5 mins after the full picture appears, the set operates fine and will continue to do so until switched off and left to go cold.