Can a laptop's screen, keyboard and touchpad be used for a desktop?

All three components normally use different interfaces that are not compatible with a normal desktop.

However, you may be able to use software solutions like remote desktop, VNC or Synergy to control your desktop from your laptop.

Alternatively, you might be able to use some micro-controller and a bread-board to rig a adapter to make these components work with a desktop. Hint: most touchpads now use the USB interface for communication.