When you install a multi-port serial adapter on Windows 2000-based computer, the COM port numbers (COM3, COM4, COMx, and so on) that are assigned to the serial devices are registered in a COM port database. If the multi-port serial controller does not work, or if you remove it from the computer and then install a new multi-port serial adapter, the multi-port serial controller may use COM port numbers that start with the next available COM port number instead of re-using the missing or removed COM ports.
Missing COM ports are maintained to accommodate certain functions that are tied to specific ports. Microsoft recommends that you do not allow those ports to be claimed by another serial adapter, either temporarily or permanently.Before you install another multi-port serial adapter, use Device Manager or the Add/Remove Hardware tool to uninstall the previous adapter when it is still in the computer. When you do this, the assigned COM ports are unregistered and the new adapter can re-use the COM ports. To do this:
Click Start, click Settings, and then click Control Panel.
Double-click Add/Remove Hardware.
Click Uninstall/Unplug a device.
Click Uninstall a Device.
In the list of devices, locate the multi-port serial adapter that you want to uninstall, and then click Next.
NOTE: Do not uninstall the individual COM port devices, they are removed automatically when you uninstall the main serial adapter.
Click Yes, I want to uninstall this device, and then click Next.
If the adapter does not work and is no longer seen by Windows, or if you physically removed the adapter from the computer, it becomes a "hidden device" and you must click to select the Show hidden devices checkbox in the list of devices from step 5. When you do this, you can remove the adapter. After you remove the adapter, you must also remove each individual COM port device. To do this, you must restart the Add/Remove Hardware tool for each port that you want to remove. After you uninstall all of the COM ports, you can use them when you add a new serial controller.