Did you try to unplug the scanner and reboot the computer?
If it will reboot, don't plug the scanner in while powered up. Turn off the computer, plug in the scanner, then reboot.
I waas installing a Canon scanner. I downloaded the software from the CD. Then, per instructions, I connected the scanner to the computer via the USB port. Just as I plugged it in, my computer went dead and I can't revive it. While I suppose my next step is the computer hospital, I thought I'd post this to see if anyone knows of any magic I might try. Thanks, grandpaw