|When you move your mouse cursor around the area where the line is, does the green line appear above or below the cursor?|
if the line appears ABOVE the cursor then a green line usually indicates
a failure of the screen, which can easily be replaced
a faulire of the gpu - possibly overheating - can also be fixed with some compressed air or removal of the CPU heatsink assembly and reapplying the thermal compount.
But we need to know if the line appears above or below the cursor...