The more devices added, the trickier this becomes. Examine each card, read each manual, or call the dealer or manufacturer to determine the default card setup and how to change these defaults if necessary. Microsoft, Inc., provides a good diagnostic program for the latter purpose called msd.exe . This program normally is located in the DOS directory on your hard drive. Then refer to the modem documentation for the correct procedure to reconfigure its COM port and IRQ settings, usually by flipping DIP switches or repositioning small jumpers between pins on the modem card itself.
Modems use IRQs to signal the computer that data has been received or sent.
Insure that no other device is using the same IRQ as the modem. On many PCs, IRQ5 is assigned to LPT2, the second printer port. If a second printer is not in use, IRQ5 might be a good choice for the modem. Next, select COM3. Then click the Advanced button.