This is simply not true. If it were, then a monitor at the equator would be ruined merely by rotating it to face east instead of west, or north instead of south. They would have needed to sell four different monitors, to accommodate customers who were going to face their monitors in different directions. Even away from the equator most of the magnetic field points north/south rather than into or away from the Earth. More likely vibration during shipping defocused your monitor somewhat; a TV–repair shop probably could have fixed it.