you sure that model number is correct. cannot find it on samsungs website. Anyway, try resetting the tv.
I have a Samsung LNT 4801f and I just installed the firmware upgrade to v. 1008.3, and now my picture is horribly degraded and barely discernible on HDMI and VGA inputs, it not all inputs. How can I fix it or re-install the old firmware? I can't find it online. I think it was v. 1003.