If your serial mouse is not working, following these easy steps will make it to work.

Note. You must be able to save your changes, or else, you'll have to do this each time you start your computer. To save your changes, see the tutorial on this section.

Tools and Materials
A text editor (vi, KWrite, etc)
The file xorg.conf. Find it in the /etc/X11/ directory.

Steps
Open the file and find the section "Core Pointer's InputDevice section" on line 262.

1.-Find the line

# ThinkingMouse ThinkingMousePS/2 Xqueue
Option "Protocol" "IMPS/2"

Replace IMPS/2 with Auto, so the line now will be:
Option "Protocol" "Auto"

2.-Find the line (below the line you've just edited):

Option "Device" "/dev/mouse"
# Option "Device" "/dev/psaux"
# Option "Device" "/dev/ttyS0"
# Option "Device" "/dev/ttyS1"

Put a # mark at the beginning of the line, so the line will be:
# Option "Device" "/dev/mouse"

Now remove the # mark in the line
# Option "Device" "/dev/ttyS0"

So the block will be
# Option "Device" "/dev/mouse"
# Option "Device" "/dev/psaux"
Option "Device" "/dev/ttyS0"
# Option "Device" "/dev/ttyS1"

3.- Save the changes, and exit.

Don't forget to save your changes! (see the tutorial about saving changes)

If you did it under the graphical interface, reboot the computer. If you did it under the console mode, simply type startx.

If something is not working properly, for example, the scroll wheel does not work, change "Auto" for "IntelliMouse" in the step 1:
Option "Protocol" "IntelliMouse"