Vista + Word 2007 keyboard shortcut problem

[Brownit]

I have assigned the keyboard shortcut of Alt+m to insert the em dash in Word 2007, which worked fine for a short time. However, it has since stopped working. Now, when I hit Alt+m it minimizes the open window, but only in Word. The same combination doesn't seem to affect other programs, such as Acrobat.

I searched through various Lenovo/Vista help articles on keyboard shortcuts and can't find any reference to an existing Alt+m shortcut. Has anyone else experienced similar problems or have any advice on how to remove the minimize shortcut and reassign my Word shortcut?