these are not the fix, they are suggestions:
1) center your screen, usually knobs below the monitor or in advanced ones the software in the monitor's menu, also, application like those with video cards or in windows can do this.
2) run a video/dvd application and change your screen aspect ratios. If you don't have a media player you can use some online video sites to do this.
3) if the above two don't work, use a blackout/black screen saver on it for some time or you can also run a white one. Putting it into sleep mode is a similar thing as well.
4) if all fails, again put it in the dual mode, maybe it'll correct itself.