picture goes black 10 seconds after welcome screen and channel number?

I have a Polaroid TLA-01511c flat screen LCD 15" tv. The Polaroid logo comes on and then the channel indicator and then the picture comes on for about 10 seconds and then goes black. I can't see the picture when I shine a flashlight on the screen. I have replaced the two 1000 uf caps on the main board which didn't change anything. Which of the two circuit boards would I have to replace? There are 7 470 uf caps on the main board some of have slightly bulged tops