I mean the part of the graphics card actually responsible for outputting to the monitor, which wouldn't be caught in a screenshot.
If you don't have another monitor to test on, see if your current one has any calibration settings to offset the picture. If the yellow line moves with the picture offset, then there is a fault with your computer. If the yellow line remains, it may be an issue with the monitor itself.
I imagine that this can also be tested without the computer simply by turning the monitor on with no computer attached