blue vertical line appearing on Latitude D505 laptop screen

recently a blue vertical line decided to adorm my laptop display. it looks like it's one pixel wide and goes from extreme top to bottom.

 

it is visible mostly when the background colour is a midtone colour (i.e. grey) . for pure black or white, it's not visible.

 

i've tried lowering the display settings to 800x600, lower colour range, etc but it appears the exact same each time.

 

when i do a "prnt scrn" to paste into mspaint, it does not get included in the screen capture.

 

any ideas?