Oh dear...
This is a VERY old machine. Over 20 years old!
The software to control this machine is here
viewtopic.php?f=46&t=3288 under "StarTurn very old DOS software"
[edit: fixed the link to old s/w]
https://website.denford.ltd.uk/support/9 ... s-software
Remember that this machine was built event before Windows95 so you MUST get an old computer that is running DOS6.2 and has a floppy disk drive. The software will NOT run in windows, even in a DOSBOX in windows.
If you can find this computer, then copy the "StarTurn very old DOS software" files onto a floppy disk and run the INSTALL.COM program. This will install the software so you can run the machine.
A diagram of the cable you need to connect the Starturn to an IBM PC can be found here
viewtopic.php?f=15&t=172&p=457&hilit=cable#p457
If the software 'Finds' the machine via RS232 it will display the CNC program. If the software does NOT find the machine (because the cable is disconnected or the machine is faulty) it will show something like "Dongle not found" or "Security key not Connected)
I really think that this machine is too old to repair and I think you will have VERY BIG PROBLEMS in trying to get this machine to work.
Good luck!