Trying to change the font freezes my computer?!?

My Microsoft Word 2007 just started doing this thing very recently where it freezes every time I try to change the font. I'm trying to write a paper, and my professor wants a particular font, so I need to figure out how to fix this within the next few days. I have Windows Vista, if that means anything. I'm not a computer wiz, so I'm not sure what factors could contribute to this happening. It will let me change the font size, it will let me change it to bold or italics, but when I try to click on the box where the font name is to choose a different one, it completely freezes and I have to restart my computer. EVERY TIME! Someone suggested it could be a particular font that I'm trying to change it to that's doing this, but I can't even click a font because none of the font names show up, do you know what I mean? I just click it, nothing happens, and everything freezes. HELP! Also, I'm trying to change it from Calibri(Body) to Arial, if that means anything. If you can help me, MANY thanks to you!