Presumably you have checked the connection is sound - no broken wires or such.
Have you checked the BIOS to see if there is anything there?
If it is still under warranty (or Dell feel kind) you could ask for advice click here
Fujitsu Lifebook P727 laptop review
Microsoft Paint set to die after 32 years
Mac power user tips and hidden tricks
Comment désactiver la saisie intuitive et paramétrer votre clavier ?