Get-FileHash </path/to/ISO>
, and compare the output to the contents of the SHA256 checksum file. This will tell you if you had a valid download, and the ISO wasn't corrupted in transit.Then the problem is likely your hardware is incompatible with the BTX bootloader. Try installing 11.1 first, which uses GRUB. Then once you've achieved a working installation, upgrade within the system to 12.0-U2.
Another thing to try: Set the boot device type to BIOS or LEGACY, and create your boot media for BIOS boot. I'm not familiar with the Pro Desk 400 myself, but I have seen some systems that are fussy about the boot device type. Also, make certain you have enabled whatever you need in bios to make certain you can boot from a flash drive. Some systems require a specific setting for this.
No, that is not what I mean.With BIOS boot you mean MBR in stead of GPT UEFI? Can you boot FreeBSD from an MBR USB device?
No, that is not what I mean.
When you run the installer to create a boot device from the ISO that you downloaded, you have the option to create a BIOS boot device or a UEFI boot device. Try telling it to create a BIOS boot device. Also, you will have to set BIOS boot in your motherboard bios (on some boards it is called LEGACY.)
For instance, my Supermicro X9SCM board is fussy about which devices will work with UEFI boot - some work OK, but others do not. I don't know why this is and have never bothered to find out. I am currently booting from an SSD that was set up for BIOS boot, and it works just fine.