You probably have blown a chip inside the unit.  
 
If an output has been shorted, overloaded, or connected to a voltage source, even if for an instant it will blow the chip. This is usually caused by installing a DC device backwards (- to + or + to – terminals),  passing any kind of voltage into the outputs 3 – 8, or touching the terminals of the outputs together.  Signs of a blown chip are one or more outputs staying on indefinitely, or outputs not responding at all yet everything else seems fine.
 
Have no fear! They are inexpensive and easy to replace.