John,

I would just do the following:

Unplug the connection to the power line and to the computer.

"Remove" the HP software that you installed completely. Then read again the instructions in the scanner guide - follow the "sequence" of software installation or connecting plugs in toto "first is first, then down to the "power on" and/or reboot.

This should work. Yes make sure also that you plug all the wires "snuggly not being too much pressure" when connecting them.

Others might give you some suggestions based on their experiences.

Good luck.