There could be a problem with the port settings, or the port voltages.
Check the PC's BIOS to make sure it is configured as a bi-directional port.
Check the port pins voltage output for 0 volts and 5 volts.
Make sure that TurboCNC is configured correctly, that each signal pin is outputting the correct high/low signal level.
Try a different computer. Be careful, though. If there is a problem with the engraver's electronics, it could damage the computer.