Out of curiosity, was it an optical mouse? because those will not run on serial ports unless they have a source of external power. Serial ports do not provide power on their own for optical mice, that sort of thing came into effect with ps/2 and usb ports, at least as far as mice are concerned. So if you plan on using a mouse on a serial port you're either stuck with a standard ball mouse or you'll need an optical mouse made for serial ports.