when key is turned there is a single click and then nothing happens.
Where do you hear this click coming from ? Before you replace parts you should test the electrical circuits , if you don't know how i suggest you take it to a qualified repair shop .
Viewing wiring diagrams to see what all is involved in the starting of the vehicle , reading how it's suppose to work in factory service repair manual .
Moving the ignition switch to the START position sends a 12-volt signal to the engine control module (ECM) to command starting. Battery voltage also travels through the switch side of the Run/Crank relay then through the clutch switch, if equipped with manual transmission, and on through the coil side of the Starter relay and then to the ECM. The ECM receives class 2 information from the vehicle theft deterrent (VTD) and transmission control module (TCM) to verify that all parameters are met for starting. When all parameters are met the ECM grounds the control circuit of the Starter relay closing the switch providing battery voltage to the starter solenoid through a 30 A Maxi-Fuse.
Are the battery cables good ? Voltage drop testing
Starter Voltage Drop
Test the control side of the circuit at the relay . Free wiring diagrams here http://www.bbbind.com/free-tsb
Enter vehicle info. year , make , model an engine size . Under system click on engine .Then under subsystem click on starting . Click the search button then the blue link . Pretty complex looking isn't it . Using a factory scan tool at the dealer makes diagnosing a lot simpler . Can view data to the PCM , start signal from the ignition switch , Starter relay control , see input from transmission park neutral safety switch .