I assume you're using Windows? Is it XP, 7? 8?
Here's previous advice given by Richard, a Canon product export, that might apply:
This sounds like the driver for your camera is corrupted. You should be able to resolve this by removing, then reinstalling the driver.
With your camera connected and turned on in the playback mode:
1- Right-Click on "Computer" (in the menu) and choose "Properties".
2- In the upper left-hand corner, click on the "Device Manager" link.
3- Once in Device Manager, find the "Portable Devices" group and click on the "+" sign in front of it.
4- If you see your PowerShot camera listed, right-click on it and choose "Uninstall" and allow the "uninstall" to proceed.
5- Now turn the camera off. Wait a few seconds and then turn your camera on.
from: http://forums.usa.canon.com/t5/PowerShot/SD750-no-autoplay-in-Windows-7/m-p/6445/highlight/true#M161
