What is windoes doing?

[dwight]

I have a question. I use the USB port for serial. In my program, I use a fixed com port. When going to the control panel, I find that I see (in use) tags on some of the com ports. I'm the only one currently using the com ports but recently another (in use) showed up, requiring me to modify my program to use another com port. How does one unuse a com port? how do I find out what is using it so I can stop it? I'm using windows 7 professional. Has anyone else had this problem?
Dwight