If you know how to, check your bios when you first power up your computer. The com ports might be set to auto on the newer pc's and the program requires a dedicated com port number.
The way to reach the bios on most pc's varies. Here are a few to try.

Watch the top right of the screen.
hit F-2, or del, or crtl-alt-enter when you see the info
F10 on compaqs when you see a blinking cursor in the corner

Hope this helps
Ron