To turn on Serial Keys
Serial Keys is designed for people who have difficulty using the computer's standard keyboard or mouse. Serial Keys provides support so that alternative input devices, such as single switch or puff and sip devices, can be plugged into the computer's serial port.
Open Accessibility Options
On the General tab, under SerialKey devices, select Use Serial Keys.
To turn off Serial Keys, clear the Use Serial Keys check box.
To use Serial Keys, Fast User Switching must be turned off. (Fast User Switching is only available on Windows XP Home Edition and Windows XP Professional when it is not joined to a domain)
For information about turning off Fast User Switching, click Related Topics.
To open Accessibility Options, click Start, click Control Panel, and then click Accessibility Options.
For more information about changing Serial Keys options, click Related Topics.