One problem could be that the serial port in Windows is set for HW flow control.
Go to "Start Menu" -> "Settings" -> "Control Panel" -> "System" -> "Hardware" -> "Device Manager" -> "Ports" -> "Com1" -> "Port Settings" and set "Flow Control" to "None" and hit "OK".
You may also need to run the old program in "Compatibility Mode", though I think not since you already can send to the laptop ok, and the laptop can talk to the machine ok.
Your most likely problem (given the info you posted already) was already mentioned - voltage levels. Newer PCs use RS-232 transceivers that "charge-pump" from 3.3V to get about 6 to 7 volt signal levels on the external port. This is close to the minimum input requirement of old equipment based on older RS-232 specifications (e.g. RS-232C).
In this last case - you might look at adding an RS-232 Repeater, like these at B&B Electronics
One of these should solve your problem.