How about telling us the method of playback e.g. Automatic, directshow filters (including which filters), windows media player engine, quicktime etc. I'm pretty sure you should know where to look for this info by now.
Also, which graphics card? Check your driver settings and let applications have as much control as possible compared to the card's drivers.
It sounds like you might be running a specific output resolution with ffdshow, or overriding an application's (MC's) settings with your graphics card's drivers.
Finally, to recentre a zoomed or offset picture, use the OSD. While playing, use the up or down arrows repeatedly until you see the off-centre measures of the vertical and horizontal axes. Use the left and right arrows to adjust. You have to do this separately for horizontal and vertical.