When did this happen?
Has this happened before?
If you have an external monitor that you can use, that has a VGA/DVI/HDMI input, then hook your laptop up to that to find out if there is a problem with your laptop screen or your hardware.
Try booting into Safe Mode by pressing F8 when you restart your PC. Cause it will use minimum graphics drivers and see if it does the same blue line thing.
If that doesn't work then try a system restore because you may have installed new drivers that may have somehow messed your graphics up.
If not then get back to me :) :)
Tell me how it goes :)