I would start by updating the video driver. What kind of video card does the computer have?
It could be the refresh rate. Right click on the desktop and hit personalize, then display, then screen resolution. Click on monitor 1 in the top and hit advanced then hit monitor. Check that the refresh rate is 60hz. Then check again for monitor 2.
it's a GTX 260 and the latest drivers, and both the refresh rates are at 60