Terrible picture on my 55411

I recently bought a used ws-55411 and when I seen the picture at the sellers home it was outstanding. When I got home and hooked it up I was shocked by a horrible picture. I have it hooked up to digital cable service through component connections into the dtv input of the television. The picture is horrible with the cable signal and is equally bad when viewing a dvd. I tried the convergence fix and it appears to be in order. Any help