If they recently worked on it, they may have jolted the LCD ribbon cable and it needs reseating or replacement.

Graphics/Display Starting To Go Bad...?Lines in the monitor usually preclude problems.. STart by checking the screen resolution to make sure it's correct. Next, look for an updated driver and install it.. It can sometimes rectify the problem for a while..

I've got an old Windows ME computer which has good days and bad days. The graphics are headed out... Some days it will start just fine.. Others, it looks worse than your pictures.. Multiple colored lines.. Parts of the screen turning black..

Hope this helps.