How to enable the touchpad on a Compaq Presario

You will have to disassemble the entire laptop to get at that.

• The first step is removing the bezel above the keyboard.
• Then remove all screws from the bottom of the laptop.
• Then carefully pry the bottom panel off.
• The touchpad should be exposed.

Here is a thorough video on disassembling an Acer laptop

Pressing the Fn key does not send any keycode to the operating system, therefore you cannot fake pressing the Fn key.

However, some Fn+another key combinations send keycodes. For example, the play/pause/next/prev key combos always send keycodes

From a terminal, you can run the xev program, which opens a simple window. You can now press various keys and key combos and the keycodes received by X11 will be shown in the terminal. You can press Fn+F8 and see if xev shows any output

Unfortunately, on most laptops the 'disable touchpad' key combo is handled directly by the hardware, so you must find another way to disable the touchpad.

If you are using a Synaptics touchpad, you should look at synclient or syndaemon. For example, this article says that synclient TouchpadOff=1 turns off the touchpad and synclient TouchpadOff=0 turns it on