If you get a PORT ALREADY OPEN error when trying to establish a dial-up connection, that's Window's way of telling you some other device is using the modem

If some other device is actually using the modem (such as a voice/fax program or you are already on a dial-up connection), the solution is to terminate the other task, or to disable auto-answer features in its software.

Sometimes, Windows gets confused, and it may seem like a reboot is the only answer. With Windows 95/98 in most cases, you can re-gain access to the port by terminating the rnaapp Task:

Press CONTROL, ALT & DELETE - this will bring up the Windows Task Bar Close Program box

Look for the Rnaapp task, select it, and then click End Task.