Joel,
HP scanners are very difficult to get going, but great once going.
I have a 5100C that takes several installs to get to work, meaning that
several reboots seem to be the trick.
Usually 3 or 4.
Have not pinned down the optimum method, but I usually unplug everything and
install the software, connect hardware and reboot.
Uninstall/install reboot.
Reboot.
Reboot.
Somewhere inbetween or perhaps the next day, it decides to recognize the
hardware.
Now I have cloned my o/s and that install works everytime. Perhaps a
registry backup from when it was working may work for you.

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