iPhoto won't import photos, doesn't detect camera

I've never had a problem uploading pictures from either one of my Canon digital cameras. However, when I now connect either camera to my computer via a USB cord, the drive doesn't appear anywhere and iPhoto doesn't recognize the camera, nor does it prompt me to import the photos. When I tried the Image Capture software, it told me that nothing was connected. The CF card is fine (it reads on a digital picture frame), and the USB connection is fine (it detected a video camera). I couldn't drag images from the camera to anywhere else, since the computer doesn't realize the camera is connected. (And yes, the camera is on and all camera settings are as they usually are.)

Any thoughts?