XPS One 2710, Windows 10 update, no display

Hey, maybe you guys can help me.

My loved XPS had a recent Windows 10 update. After the update there was a screen "Diagnoses is running". PC turned off, if I start it now, the display goes on, all the fans are running, but it won't even boot into BIOS.

USB is also dead. I removed everything, like DVD, HDD - same result.

If I also remove the RAM it gives me a beep as mentioned in the manual. Therefore I suggest the motherboard is OK. I also guess the power supply is OK, since all fans are running.

I can use the display if I connect a PC via HDMI-in so I guess the display works.

I also reset the jumper of the BIOS and the battery for a day.

Any suggestions what else I can do? It's really difficult since I don't see a XPS 8930, 2TB NVMe upgrade and don't have a signal with the USB.

Andy