The water inlet valve is located behind your refrigerator. Find the water supply line coming into the valve and turn it off at the source (typically under the sink). Disconnect the supply line. Remove the screws that secure the inlet valve in place.
Before testing the water inlet valve, unplug the refrigerator to avoid an electrical shock hazard.
The water inlet valve is connected by two wires.
Label the wire placement on the water inlet valve before disconnecting
the wires. The wires are connected to the terminals with slip
on connectors. Firmly pull the connectors off of the terminals
(do not pull on the wire). You may need to use a pair of needle-nose
pliers to remove the connectors. Inspect the connectors and the
terminals for corrosion. If the connectors are corroded they should
be replaced.
Before testing the water inlet valve, unplug the refrigerator to avoid an electrical shock hazard. 
