Cannot Access Time Capsule Backup

I upgraded my Mac Mini Late 2012 (2.3 GHz Intel Core i7) to High Sierra from Mountain Lion (OS 10.8.5). I backed up everything on my Time Capsule (A1470) 2 TB before doing so. I then realized I needed to go back to Mountain Lion, so I attempted to boot from the TC. It asked for my password, but it didn't work. This has always been the password, so I know it's correct. I researched this issue and there can be a password problem due to outdated firmware on the TC. So, I updated the firmware on the TC and reset the password. I also did a hard reset (twice) on the TC. All should have been fixed in theory, but now I still cannot boot from the TC. It's not showing up.

When I connect the TC to my Macbook Pro (Yosemite OS 10.10.5) and Mac Mini (High Sierra), all I see is a CD icon named "EasySuite" on the left toolbar. It does show up under Airport Utility, however.

How can I boot from the TC? Is the drive cashed totally? Or is there some other issue I'm missing?