I'm afraid that is just about as far as I can go.
If cables and settings and setup are all perfect, the only thing left is that the machine is corrupted, or set to block/disable all access.
If that is the case, the only remaining thing to do is reset the device.
But....
The machine is ancient, it has no USB ports, the only way to even connect to it is via Serial cable, and with a software that is not available to download (Yay old proprietary setups!!!) And even if you had the software, you would need an old PC with a Serial port just to hook into it, so Windows XP or Windows 2000 would also be needed.
With no maintenance agreement, it would cost more than you have into the device in total at this point and there are no guarantees, you might have come upon the reason it was in the auction, it very easily could be broken beyond repair.
For reference, these are the top phones from when this device was current ;-)
If you could find how to reset the machine NVM's you could likely get access assuming it is not actually physically broken, but you won't find that information here, even if I had it, I could not post it, but the internet is a vast place with many resources.