Need to re-image my Dell Venue 8 Pro

This is a pretty long explanation, but I hope someone can help me!

I have a 32gb Venue 8 Pro, and when I got it 12 months ago, I immediately made a recovery "disk" onto a MicroSD card, and deleted the recovery partition to free up space.  I put the MicroSD card into a desk drawer, and went on about my business...

This weekend, I decided that I want to sell the Venue 8 Pro, so I hauled out the MicroSD card, popped it into the Venue 8 Pro, and went into the Recovery menu inside Windows 8.1.  I started the recovery, but it immediately told me that I didn't have valid recovery media inserted.  I popped the card out and back in a couple of times, but it didn't matter.

I gave up on the Recovery app, and went into the Advanced Options where I could do a "reset."  The device rebooted, and showed me a menu where I could pick a backup "image" to restore from.  It showed me an image with a time/date stamp that corresponded to the recovery image I had made a year ago, so I thought that all was well. I picked that image, told it to start, and the system appeared to be restoring successfully.  Part way through, it rebooted, and now I get "internal hard drive not found" errors.  

I have downloaded other people's factory Recovery images from various online forums, and I have the ability to make a recovery USB drive.  I did just that, using Rufus to turn an .img file into a bootable USB drive.  However, the DV8P never attempts to boot from the drive (when I connect it via a USB OTG cable).

If I go into the BIOS, and look at the boot options menu, I notice that the "Boot Option Priorities" is greyed out.  I can't click/tap on it and select any options for it.  The other four menu options are available to me, just not "Boot Option Priorities."   I assume I need to do something to get the DV8P to see a bootable USB drive, right?

At this point, I'm all for any option that allows me to make the device bootable again.  I have an external USB CD-ROM drive so that I could install from a Windows 8.1 disc, or I could make a plain old Windows 8.1 USB drive and install from that.

What's my best strategy for restoring/reimaging when I'm stuck in the state I'm in -- can't boot, don't know how to enable the correct boot options in the BIOS?

Thanks everyone!