I just bought this TV and today I noticed the black screen had three dim lights on three corners on the screen.is this normal for a LCD TV? I noticed it because I turned off the cable box and the TV stayed on.that's when I saw the 3 lights on the corners they were kind of dim but noticeable.please help

Sounds like "flashlighting". Try turning down the backlight setting. It might help. Otherwise you could try returning or exchanging it, since flashlighting (unless really bad) isn't usually covered under warranty.