Sometimes Windows 7 won't recognise Canon cameras.
 
My camera worked on my friend's computer who has Windows 7 Professional, so we knew the camera wasn't faulty. I was simply unable to find a driver to download, and neither could Windows Update. Error code 28 plagued me in Device Manager. It was annoying. I did a firmware upgrade just in case there was some weird bizarre compatibility issue, but that did not fix it either. So I started thinking - what makes his computer different from mine, the answer was the "N" in our versions of Windows.
 
My university gave me an academic license for Windows 7 Professional "N". That "N" is important. The "N" line of Windows ships without a lot of baggage in the way of media libraries, Windows Media Player, codecs, and other whatnots that take up gobs of disk space, which suits me fine. Often a business will get "N" editions too simply because it's less crap on the computers that IT have to manage.
 
The problem is, a lot of Canon cameras like to be able to talk "PTP" over USB to the computer, and the "N" line of Windows 7 also leaves this out. If you're having problems getting Windows to recognise the camera (but Device Manager sees it), consider heading over to Description of the Windows Media Feature Pack for Windows 7 N and for Windows 7 KN at the Microsoft Knowledge Base and see if the ~300MB media pack will assist you.