IBM ThinkPad 755CX Manual page 233

Problem
The mouse or pointing
device does not work.
All or some keys on the
external numeric keypad
do not work.
All or some keys on the
external keyboard do not
work.
A number appears when
you type an alphabetic
character.
Verify that the mouse or pointing-device cable is securely connected to the
computer.
Try using the TrackPoint III. If the TrackPoint III works, suspect the
externally attached pointing device.
If you are using Windows, make sure Computer is set as MS-DOS System
with APM. See page 177.
If you are using mouse that is not compatible with the IBM PS/2 Mouse,
disable the TrackPoint III using the ThinkPad Features program.
1. For OS/2 and Windows, see page 36. Select Setup,
Keyboard/Pointing Device; then click on disable for the TrackPoint III.
2. For DOS, see page 41.
Verify that the external numeric keypad is correctly connected to the computer.
Verify that:
The keyboard connector is connected to the correct side of the
keyboard/mouse connector.
The keyboard/mouse connector is correctly connected to the computer.
If the preceding items are correct, disconnect the keyboard/mouse connector
from the computer and verify that the operation of the system keyboard is
correct. If the system keyboard works, have the keyboard/mouse connector or
the external keyboard serviced.
The Numeric Lock indicator is on. Press and hold Shift; then press NumLk.
What If Your Computer Does Not Work?
Action
Chapter 8. Solving Computer Problems
217