Windows recovery environment can not be reached by the BIOS

Windows10 of my Dell Precision T3620 is somehow broken. Charging stops after the Dell logo and displays only a blank gray screen with a flashing mouse arrow (meaning no Windows logo is displayed).

I'm trying to recover the operating system from Dell's own recovery partition – but it fails as well.

Getting started in the BIOS (F12 on my machine) I see all the usual BIOS administration options and so-called Windows Boot Manager – Where should be the option to restore the operating system in my understanding. But to choose Windows Boot Manager I see again the gray screen and the flashing mouse.

Changing the boot mode from UEFI to Legacy, I see after the selection Windows Boot Manager Windows logo appears for a short time – but then again the gray screen.

I do not have a recovery media from Dell.

Q: What are the options for running OS recovery that could be helpful in my case?