I have a US Robotics 56 K modem that the device manager properties says is on Comm 3. I use for a paging program. It used to work. The paging program says that comm port is either busy or not responding. In Control panel/Modem when I try to test the modem it says can't open comm port. The paging program says comm 1 or 2 are responding. How do I change the modem to Comm 1 or 2. Why can't Comm 3 be opened?