I have an LG 42 inch Flat screen that i've been watching all day, now there is a small red line on the side..

Question

of the screen why has this happened and what should i do??

Answer 1

If its an LCD then you will have either a bad controller circuit board assembly or a bad LCD Panel (yes--the panel).  If its a plasma then its either a buffer or logic circuit board--or at the worst--A bad panel (yes the panel again).

I hope its under warranty otherwise you could expect a minimum of $350 (if you're REALLY lucky).  If its the panel then its not worth fixing--sometimes not even under warranty--they'll exchange it.