Hello Roland,
So you get no picture at all when connected to a display. No startup picture with Beomaster 5 (and Beomaster 5 recovery)?
Did it just stop working?
Can you get into the bios?
I use an old Logitech USB keybord and mouse (K520 / M310). Start the beomaster with the button on the back and pres "Del" several times to log into the bios.
Then try booting with Hiren's BootCD From USB Flash Drive (USB Pen Drive).
https://www.hiren.info/pages/bootcd-on-usb-disk
If it works, then you should be able to re-install. I prefer to make a clean installation with the service tool and to update via bang & olufsen servers.
The servicetool is a 4 GB usb flash drive, which I might be able to transfer to you, if needed.
Unfortunately, the motherboards often fail, but it could also be the harddrive.
If it is the standard mechanical drive, then you should be able to hear or feel it spinning. The harddrive is pretty easy to replace with a SSD drive, eg. WD Blue Nand 1TB SSD. SSD's with Marvell Controller 88SS1074 works.
I have attached the service manual for Beosound 5 / Beomaster 5 for info on how to replace motherboard and harddrive.
You might be able to finde a new (old stock) or used motherboard on eBay.
Look for VIA EPIA EX15000G like this:
https://theretroweb.com/motherboards/s/via-epia-ex
https://cdn.viaembedded.com/eol_products/docs/epia-ex/datasheet/VIA+EPIA+EX_datasheet_v120508.pdf
If needed, I can help you with installation tips for motherboard and SSD.
Best regards,
Jens