Boot stuck Dell Logo

As a short preface:
We are currently planning a major conversion of our environment to Dell devices.
To test the use of the CCTK, we used an existing Dell Optiplex 7460 All-In-One whose “ProSupport Plus” expired in December 2024. 
This was also successful to the extent that all desired BIOS settings were applied correctly. This process was repeated several times with identical settings and the BIOS was reset in between. 

Since the last attempt, the All-In-One has been stuck in the boot screen with the Dell logo.

You can press F2 and the message “Preparing to enter Setup...” appears, but it does not open, but remains with this message. 

You can press F12 and the message “Pepaing one-time boot menu...” appears, but it does not open and remains with this message. 

The attempt to import a recovery bios “BIOS_IMG.rcv” using the key combination “Ctrl-Esc” has the same result. Apparently the boot environment is started from the USB stick in this case, as “F12 Boot Options” appears in the top right corner depending on the BIOS version used.

In these tests, only one keyboard is connected to the All-In-One via USB and the power cable.

In all cases, the All-in-One can be restarted via the keyboard using “Ctrl-Alt-Del”.
None of these steps resulted in a change.

An attempt was made to reset the BIOS via the BIOS reset jumper “JMP1” / “Jumper for service mode / Jumper for deleting the password / Jumper for deleting the CMOS” on the mainboard.
password / jumper for deleting the CMOS” on the mainboard and the password was also deleted in the same way.
Neither caused any change.
In addition, the BIOS battery was removed (> 4h), the SSD removed and the RAM (2* 8GB) installed individually, the positions swapped and swapped from another device.

Unfortunately, as already written, the All-in-One has not been supported since December 2024.
Could you perhaps still give me further tips on what I could do to get the Dell Optiplex 7460 All-In-One working again?