Unable to add ANY video files to Library??

For some reason I am unable to add any format of video to my iTunes library. I'm using OS X 10.4.6 and iTunes 7.2. When I try to add any sort of video file (be it avi, mov, or m4p to my library, the loading bar pops up for a split second (sometimes) and then nothing happens. I've tried using "Add to Library" I've tried dragging and dropping, I've tried the "open with" command. I've tried many different video files of all sizes, and nothing seems to work. I restarted my computer, I re-installed iTunes, I unplugged all external hard drives and peripherals, and just about everything else I could think of. The file simply does not appear in the library listing or copy to the library directory.

Suggestions?