You probably have a PS/2 mouse connection, rather than a serial (*see image). I suggest you open the Device Manager, select your mouse and click the "Remove" button. Then restart your computer.
(Note: If your mouse is connected with a USB connection (*see image), just unplug it, then replug it in. You don't need to shut down your computer)
Details:
Right click on "My computer", choose "Properties".
When the System Properties window opens, click the "Device Manager" tab.
Scroll to your mouse, and click the + sign to the left. Select the mouse, and click the "Remove" button. OK the warning dialog box.
At this point, the mouse won't work of course, so you will need to use the Tab and Arrow keys to move the cursor. When you choice is selected, press the enter key. Watch the buttons to see which is selected.
Select and press "Enter" on the OK button, or use the Ctrl + Alt + Delete keys (all pressed together) to open the "Close Programs" window.
Use the Arrow keys to scroll to "System Properties" and then the tab key to highlight the "End Task" button. When it is highlighted, press the Enter Key.
Press Control + ESC to open the Start Menu. Use the Arrow keys to move up to the "Shut down" button, then the Enter key to open the Shut down dialog box. Select Restart, then press Enter.
At start up, Windows will recognize the connected mouse and install the drivers for it.
Hopefully, this will stop it from looking for a serial connected mouse, unless of course your mouse actually is a serial mouse. But, if it is, Windows would install the driver for it, or prompt you for the driver installation disk.
*Image of serial, USB, and PS/2 connections:
see image
