I would turn off your printer and computer first of all.
Unplug the USB connection for the printer and then turn on your computer.
Once the computer is at the desktop, then turn on the printer and plug-in the USB printer connection. This may solve the problem.
If not, go to the Device Manager and "Uninstall" the driver and reboot then install the driver again.
Are you running 32 bit or 64 bit Windows 7?
You may have to do a new clean install to really get it working right.
Here is the driver page for your printer:
Canon Drivers