First of all: I have a running MS-DOS 6.22 OS on that PC running but I'm not able to boot into Windows NT.

System Information:

Main Processor: AMD Am5x86, 133.6 MHz
Math Co-Processor: Internal
Bus Type: PCI (V2.10) + ISA
Mainboard Model: GIGABYTE GA-486AM/S https://theretroweb.com/motherboards/s/gigabyte-ga-486am
Mainboard Chipset: UMC UM8881F
First Level Cache: 16 KBytes
Second Level Cache: 256 KBytes of Asynchronous SRAM

System Memory Size: 640 KBytes
Extended Memory Size: 64,512 KBytes } Total: 64 MBytes
Shadow+Special RAM Size: 384 KBytes

Machine Type: IBM PC AT
Computer Name: Unknown
BIOS Manufacturer: Award Modular BIOS v4.50PG [11/07/95]

My steps I tried so far:

Setup with https://86box.net/:
Info: the Motherboard does not support booting from CD-ROM

• Setup the machine as similar as possible to the real PC
  The attachment 86Box_HW.Config.png is no longer available
• Create a raw image file (.img) with max. 2GB as your harddrive in 86Box => "Add New Hard Disk"
• Install MS-DOS 6.22
• Write the img file with Rufus or HDD Raw Copy Tool to the real physical HD
• Insert the HD to the PC and boot into the newly installed system => working fine with MS-DOS
• Insert the iso for Windows NT to 86Box (downloaded from https://winworldpc.com/product/windows-nt-40/40)
• Copy the content of I386 to the HD (C:\I386)
• Write the img again to the real HD
• Boot into MS-DOS
• Copy code to clipboard

  1C:\I386\WINNT.EXE /b /s:C:\I386
  

  => C:\$WIN_NT$.~BT and C:\$WIN_NT$.~LS are created (floppyless installation)
  The attachment 86Box_HD_Content.png is no longer available
• Reboot
• Should show this boot menu
  The attachment Win_NT_OS.Loader.png is no longer available
  but is not.; it shows just a blinking cursor or an error

I'm also using a SATA to IDE adapter: StarTech IDE/SATA Adapter (JMicron JM20330 Chipset)

So, MS-DOS is working fine with this method but not Windows NT 4.0. What could be wrong?

Thanks for any help,
Best regards Peter