Everything you need for your Canon PIXMA is contained in this link: PIXMA MP620
It does sound very much as though the problem is driver
-related and it's quite possible the driver disc is not a Windows 7 one.
You could also download and install your drivers
etc. first, and then try adding your printer in Start>Devices & Printers>Add a Printer.
Have a look in Device Manager to see if your printer is detected there and if you're not sure whether your printer driver has installed, you can check under Uninstall a Program in your control panel.