HMI cannot communicate with DCS

Greetings to all,

We have GE Frame 5 Gas Turbines, controlled by Mark V TMR control system under DOS. The hard disk of one of the HMIs failed and we had to replace it. After replacement, we lost the communication between HMI and DCS. The communication is done via modbus connection. We did few trials and checks; check the definition of modbus, cross reference the modbus list between HMI and DCS. The last thing we did is take the CPU of another unit and install the hard disk of this specific turbine on it, everything came back to normal. Therefore, we concluded that the issue is in the CPU, probably in the motherboard's port. The mouse was working fine, so we tried to unistall it to connect the modbus to COM1 port (used for the mouse), by removing mouse folder from the C drive and commentting out the mouse definition lines in autoexec file, the mouse pointer disappeared and nothing can be done by the keyboard.

There is a warning in the manual not to uninstall the mouse, but we have no other options in mind. Is it possible to unistall the mouse to use its port for modbus communication ? If so, how we can do that and keep the mouse pointer ?

Thank you all in advance.

Why mentionning DOS is that an <I>DOS or an HMI ?

Please clarify

Also you should read th eright GE manual like GEI-100517 all operations like serial communication physical layer installation is described

Also it is written that in case of unavaibility of any port you should create an extension ...