I did a new search and found this info for when you have a Carraige Lock situation like mine. I'll give an update once I've tried it.
HP Scanjet Scanners - How to Perform a Hard Reset
Follow the steps below to perform a hard reset on your HP Scanjet Scanner.
Power off the scanner.
Disconnect all cables from the scanner (including the Universal Serial Bus (USB), power module, Transparent Materials Adapter (TMA), and Automatic Document Feeder (ADF) cables).
Lock and then unlock the carriage shipping lock, if applicable to your product (see below).
Models with no shipping lock include: 3500c, 3570, 4070, 4070v
Models with one-time (disposable) shipping lock include: 2300c, 2400, and 3670c
Models with re-usable shipping lock include: 3400c, 4300c, 5400c, 5470c, 5490c, 7400c, 7450c and 7490c
If your product is not listed above, refer to the material that came with the product for additional shipping lock information.
Ensure the scanner is on a flat and level surface.
Plug all cables back into the scanner.
Power the scanner back on.
The hard reset is now complete.