I bought a Samsung LTN1785W LCD tv not too long ago and I am having a problem with the screen. After about 10 minutes of having the tv on, the screen starts to get progressively darker. It is like a shade is being drawn down on the screen until the whole screen is very very dark. 1) Has anyone ever encountered this before? 2) Does anyone know how to fix this or how much it would be to fix it?? Thanks in advance for any help you can offer.