Lines across the screen

If shown during the boot up process then you have a physical damaged screen.

Hi,
Its because of Over Voltage of Screen (G2) to Blue CRT.
Take off front lower cover (speaker grill) and unscrew board. There you will need to find Focus Block mounted having 6 control knobs. 3 knobs are for Focus control and 3 are for Screen volts control. Find Blue Screen control knob and turn is Counter Click Wise slightly until bluish shade disappear on screen including few blue horizontal lines.
If you select AV input to adjust that will be fine as you do not need to wait for dark-scene.

it's an lcd filter fault it's betwine lamp and screen before mirror, seems like u will need to replace it but it hard to say without look at it.

it sounds like you are seeing the vertical retrace for all three colors together (white). Its possible that all three screen adjustments (red, green, blue) are off, but I suspect a problem with the screen power supply.
there is also a recall on this set
http://esupport.sony.com/perl/news-item.pl?mdl=KP51HW40&news_id=24

It is not a bulb. It is a picture tube. If there are thin blue lines across the entire screen, not just the edges, and the picture itself looks too blue, it means that the blue picture tube is being driven too hard. This could be because the blue screen voltage is too high, the boost voltage on the blue picture tube is too low, or the video output is leaky or shorted. If the picture has what looks like blue arcs and double images on one or more sides of the picture, it means that one of your convergence IC's has burned out and needs to be replaced. These are things that should be tested and serviced by a qualified tech, so allow an experienced tech to handle it for you.

Vertical output chip has some ring cracks on leads (cold solder joints). Set is shutting brightness off to protect5 it's crts from burning a black streak across them.

clean the lens or get a new colour wheel

you know its in vertical section, try to look for a capacitor and changed it, this is more of a capacitor problem.

you have done said it vertical lines then you will have to take your tv to a tech for repairs.good luck.

i have a samsung rear projection , and it has red lines going across the screen. i put it in the back of my cuboard and went out to buty a new tv . now a few months on i got it back out to have a play with it and i coverd up the red bulb with something fireproof and now the picture is great again just that there is no red anything that is red looks a bit darker. its not great but a least its some use now and i use it in my bedroom. it mite not be much help but a least i dont have to keep it in a cuboard anymore.