My first inclination would be to see if my computer is "seeing" my scanner.
I'd connect the scanner to the computer via the USB cable, selecting USB Mass Storage, then opening Windows Explorer. You should see something showing up as a Removable Disk.
This should tell whether the computer is recognizing the scanner.
Then unplug the scanner and watch the Removable drive "disappear" on Windows Explorer. After doing so, give the scanner a few moments to go through the "Loading Favorites Lists" process and plug it back into the computer and see if it reappears in Windows Explorer as a Removable Drive (that may take a moment or two to happen).
Then start Sentinel and attempt a "Read From Scanner" and see if the corresponding drive letter shows up in the pop-up window. If it doesn't show up, though Windows Explorers as a Removable Drive, hit the Refresh button and see if that does anything.