Hi, I have two older Powershots the A560 and the later A650 IS which I really like. I also have a Canon Canoscan USB scanner and it's drivers installed. Since migrating to 64 bit windows a while ago I've had problems with the powershot drivers instal...
I solved this nasty problem: Powershots install their (oldish) driver when USB connects. Unlike my Canoscanner which has drivers shipped on CD. Camera USBs are 'discovered' as portable devices using Windoze MTP. In my case, My Win7_64 was not running...