I have tried downloading pictures from my Canon a720 to both my pc and my Mac, neither computer recognizes the camera. I am not sure what to try next.

Consider NOT connecting your camera to your computer.

The best way to download pictures from your camera to your computer involves removing the memory card from the camera and plugging it into a card reader (either built-in to the computer or connected via USB or FireWire). This is likely to be faster than connecting the camera to the computer, and won't run down your camera's batteries.

Once the card is plugged in, it will appear to your computer as a removable drive. You can use the operating system's drag&drop facility to copy pictures from the card to the computer's hard drive, the same way you copy any other files. Or you can use iPhoto (on the Mac) or any other photo cataloging program, such as Picasa ( http://picasa.google.com ) (on the Windows machine).