I have read several threads on this issue, but nothing helps me

BG: I 'inherited' an older XC605 with Win8 installed. I replaced the harddisk (as there may be a need to go back to the Win install, which I btw don't have a login to) when I return the server some day...

I can boot ubuntu-20 live/install disk and install ubuntu (server) on the (new) HD just fine

However when it comes to boot the server, I only get this

a) a beep

A few flickering cursor lines and then

Reboot and Select proper Boot Device
or Insert Boot Media in selected device and press a key



Details

System BIOS P11-A1

Authentication:
System Boot State Setup (greyed out)
Secure Boot Mode State Disabled (greyed out)
Secure Boot [DISABLED]

Security
Supervisor Password Not installed (greyed out)
User Password Not installed (greyed out)

Boot
Launch CSM [Always]
Launch PXE OPROM [Legacy] (greyed out)
Launch Storage OPROM [Legacy] (greyed out)
Launch Video OPROM [Legacy] (greyed out)

Boot Priority order
1st Boot Device [ubuntu]
1ns Boot Device [P1: HL-DT-ST-DVDRAM...]]
3rd Boot Device [Removable Devide]]
4th Boot Device [LAN]

...

Boot Menu [Enabled]
D2D Recovery [Enabled]
Quiet Boot [Enabled]


Without access to Windows (and no Windows install media) how
can I get past this?

The Ubuntu install disk (even though its name has live in the filename) that I burned does not seem to offer any live mode either