There are 4 things I would check....
1). Check any and all fuses for the 4x4 system
2). Check the controller. Should be somewhere behind the driver's side seat. There should be a little white button with a red light next to it on top. Will hte key to on and the engine not running. Push the white button. If the light blinks than it is ok. If it just lights up, I think it's toast.
3). See if the connector down below that plugs into the shift motor on the t-case is your problem. Uplug it, make sure on the male side of the connector, that there is none of the prongs pushed back enough so that it doesn't make a connection.
4). Follow these instructions and clean your electric shift motor, I did it and it worked wonders for me!! The part that really does it ,is breaking open the plastic part where the wires go into. Clean those contacts(with a fine grade sandpaper or scotch pad) and slightly bend the brushes down to make better contact. What happens is the factory grease will harden without use, and will prevent the two from contacting, not letting the computer know where it is, if the computer does not know where it is, it will go into fail safe mode and not shift. Most of the time, when this happens, people can shift fine into 4High, but wont go into 4low, they will just hear a few clicks.
Clicky:
http://www.therangerstation.com/forums/showthread.php?t=89&highlight=shift+motor
http://www.therangerstation.com/tech_library/TCaseshiftmotor.htm
Good luck!!! The best way to preserve the electric shift system is to use it!! Both 4H and 4L.