I found this solution on a different page and it fixed my camera that was having the same problem.
In the case where you get a black image, the following may be of help:
This is a common problem in older Canon
S2 IS cameras, especially ones that have not been regularly used. What happens is that the lens iris gets stuck at a small aperture. Most often you can get function back. Here's how:
Turn the camera
on in shooting mode.
Turn the mode selector to shutter priority ("Tv").
Use the four-way button on the back to set the shutter speed to 15 seconds. That's right, 15 seconds. (To do this you keep pressing the left direction on the four-way button until it goes from 1/1600 or whatever it might be all the way to 15")
Press the shutter release. Count to seven, then pop open the battery compartment.
Wait several seconds, then close the battery compartment.
You may need to repeat the above sequence several times to unstick the iris. If that does not accomplish it, you will likely have to send the camera in for repair.
Once you have it working again, you should use the camera regularly to keep it from sticking again.
This sounds like a pretty ghetto solution but it worked for me and I know it has worked for others. So before you go wasting your time writing letters, give this a shot.