I have had this set since Nov 2003 and have been very happy with it. However in the last few days in the bottom left hand side of the screen a 2mm thin black line approx 12 inches long has suddenly appeared

. It is a perfect straight line and is only removeable by changing the screen mode to cinema, which I would rather not do. Also this does not happen with all channels, most ot the telewest channels are ok but bbc1 bbc2 itv1 channel 4 channel 5 are all affected
Has anyone had this problem and can offer advice, or does anyone know a solution?
Also what is the normal warranty on toshiba televisions? I purchased this from Comet by credit card.
Thanks in advance