Manufacturing mode level 67

Plug the charger in.

On start up keep tapping either F1, F2, F10,(Be Aware that some manufacturers use F10 for system recovery!) Esc, or Del, to enter the BIOS set-up. Look for "Factory Default" or similar, and return the settings to default. Save settings and exit.

Unplug, remove the battery and press the power button for 10 seconds.
Restart.

Go to Dell support* and download/install the correct new BIOS version (flash the BIOS).
http://www.dell.com/support/drivers/us/en/04/DriversHom...