I don't know how to fix your problem. But since you are new to Linux I can give you a clue. Use a text editor to look at the file /etc/X11/XF86Config-4. This is the file for graphics and input devices. In it you will find a section for serial mouse. Mine looks like this:

Section "InputDevice"
Identifier "Serial Mouse"
Driver "mouse"
Option "Protocol" "Microsoft"
Option "Device" "/dev/ttyS0"
Option "Emulate3Buttons" "true"
Option "Emulate3Timeout" "70"
Option "SendCoreEvents" "true"
EndSection

Hope you get it to work