Just changed my alternator, battery, and crankshaft sensor on my 2004 mercury sable LS. Car ran fine for about 2 days. Won't start after that. I turn the key, and all I get a lot of engine clicking. I hear my fuel pump click on, and all my lights run as well, but the engine doesn't start. Why won't it start?
if you hear a rapid clicking and the engine is not turning over check your battery and/or battery connections. A rapid clicking (coming from the starter solenoid) is because there is not enough battery power to hold the starter solenoid down to then engage the starter. Your light and other things don't use current like the starter so they will still work. Leave your lights on when you try to start the engine and see if they go dim or stay bright.
Why did you replace your battery and alternator? you might have a draw running down your battery.