Computer Won't Boot after Updating the BIOS on a Dell Precision 5820

Here's how I solved the issue:

1. Unplug all peripherals including the keyboard, mouse, and monitor.
2. Clear the BIOS, CMOS and NVRAM by removing the CMOS battery a) Power off the computer, then unplug it b) Press and hold down the power button for 30 seconds c) Open case and remove the motherboard (nickel sized) battery d) Press and hold down the power button for 30 seconds e) Reinstall the battery f) Close up the case and connect only the keyboard, mouse, and (one) monitor g) Reboot
3. At this point, my computer would only boot to BusyBox. BusyBox gave me a "ALERT! UUID=*** does not exist. Dropping to a shell" error. My OS is installed on a NVMe PCIe SSD boot drive, and I have a single SATA file drive.
4. Reboot and enter the boot menu (hit F12 repeatedly when you see the splash screen). Go to "BIOS Setup."
   a) Under "System Configuration," set the "SATA Operation" from "RAID On" to "AHCI." b) Under "Intel VMD Technology," set to "Disabled" and uncheck the listed hard drives (PCIE0, PCIE1....).
5. Reboot.

This fixed the problem for me. The Intel VMD Technology has something to do with setting up RAID. When it was enabled, the BIOS couldn't see my PCIe boot drive.

If you're setting up a new system, you may have to tinker with the "Boot Sequence" under the "General" BIOS settings.