I'm not sure I can help but I upgraded a VMC190 a while ago. I bought software from boxford but I also had to replace the chip set (EPROMs) on the boards and do a little bit of soldering.

Is is your machine old enough to be running on the old DOS software ? Maybe it now needs the chip set too.

How are are you trying to connect to the PC, serial cable and serial port ? Mine couldn't find the machine when I tried a serial port to usb adaptor. I had to buy and older pc off ebay with a dedicated serial port at the back.