Windows 7 Not Booting--Black Screen with Flashing Cursor, then Pale Blue Screen... Rinse and Repeat.

I've searched forums on many different sites for an answer to my issue, and nobody seems to have had something similar.

I already have Windows installed, and I've used it countless times. Today, however, it refuses to work. I go through the regular steps of holding option and powering 'er up, and the screen comes up that gives me the option of either booting with Windows or OSX, but when I choose Windows, a black screen with a flashing cursor comes up for a few seconds, then the CD drive makes its whirring noises, and I get brought back to my OSX side where I can choose which user to log on as.

Only thing that's changed recently is that I did a software update over the weekend. Would that create an issue for any reason?

Thanks!