First, make sure that you have the original USB cable that came with the camera. The recent security updates to the Windows operating system and virus protection programs interfere with the camera connections.
I have seen many cases where the connection worked one day and would not work the next. Some manual set up may be required to get the camera to connect, with or without any Canon software installed. First, restart your computer. Then with the camera on and connected with the USB cable,on the computer, go to [Start] control panel, ( In Windows 7 select show all options) scanners and cameras and try to connect through the wizard. The last part of the Wizard should give you the option to choose the program to open when the camera is plugged in. If scanners and cameras does not show in control panel, click Start and in the search box, at the bottom, type in scanners and cameras and hit Enter. This should take you to the scanners and cameras box. If unsuccessful, the last place to look is in the device manager. Go to back Control Panel, double click the System icon and select Device Manager. Under the heading Imaging Devices you should find the camera, possibly with a yellow triangle with an exclamation point. Click on Imaging devices (the words will highlight), then go up and click on Action and select "scan for hardware changes". The camera may then appear under the heading. You can also delete it and allow the computer to try to provide the correct driver. Since you are trying to use the Canon software, open the program and try to connect.
You will now need to back through the Camera menu Scanner Wizard to make it Auto launch. If still no connection, plug the camera into the computer, turn the camera on and reboot the computer while it is physically connected. When the computer is back up, repeat the steps above.
While not the most popular suggestion, this one depending on your computer configuration may be the only way.
As an alternative, because of multiple intermittent compatibility issues with the camera connections and current operating systems, my other suggestion is to get an inexpensive USB memory card reader. You can take your memory card from the camera and plug it into the computer. The card will show up as a removable drive in "My Computer" or "This PC" in later versions, and you can copy the photo files to a folder on your hard drive and view and print them from Windows or even transfer them from the card into the Canon software. Personally, I prefer this method due to the simplicity and reduced wear and tear on the camera.
Please keep in mind that my diagnosis & solutions provided are directly dependent on the accuracy of your description of the problem. As with any "do it yourself" fixes, success is a "team effort", since I can't see or touch the camera, and relies on the customer's manual dexterity and ability to follow the instructions well.
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