Well, does it just click when you turn the key, or does it crank over but fail to start. If it isn't cranking over and just clicks, then it could be your starter silinoid. It could be bad ground wire. It could also be a faulty ignition relay or switch. If the battery has a full charge, then the alternator has nothing to do with it. If it cranks over but fails to start, then it is one of two things, fuel or ignition. It takes spark and fuel to fire. So, check the fuel pressure on the fuel rail first. If that's good, take a plug wire loose and put a screw driver in it and have someone crank it while you touch the metal part of the screw driver to something metal. Be careful not to touch the metal part of the screwdriver or you'll get the crap shocked out of you. Anyways, if you got spark, then you're fuel injectors are not functioning correctly. Take and ohmeter and test the wires going to the injectors. Also, check your battery cable ends for corrosion or loose contact.

it depends on your definitions of (it trys to turn on) if the engine is cranking over but it doesnt fire up then its a gas problem or fire/spark to the plugs problem.

its not the alternator..the alternator only recharges the battery and makes its own power while engine is running, the only way it could be your alternator is if the battery is dead cause the alternator didnt recharge it... you say your battery is good.. make sure the cables are tight and clean on the battery, if the engine cranks/ turning over but its doing it slowly then your battery needs more power or you got bad connections.

if you only hear clunk or clicking sounds then your battery is dead. if you hear no sounds at all and it does nothing at all then the starter is ethier jammed up or the solenoid is bad in the starter which means you need a starter cause they came together...

ill be honest with you.. the way you say it wants to turn on but it gives up.. that sounds like a dead battery. it has to crank the engine fast enough for it to fire up... and as ive said if the engine is cranking but it just doesnt fire up then you have ethier gas or spark/fire to the plugs issue.... which means you need to start doing process of elimination to figure out whats the problem.

if your engine is cranking/turning over then the first step to check as as the other person said check for spark with a screw driver.. that's first think id check cause its easy and fast.... if you have spark then its fuel related so at that point most common things are fuel pump and filter.

now if you didn't get spark (make sure its kinda dark to see it easier if this ur first time) if you didn't get spark many things can be wrong but most common is your coil. but lets go step by step so just come back and ask more questions as you get more info about whats going on with it cause we are trying to understand whats going on by how you worded it.

Battery problems firs thing i can understand, or mechanical failure..

If your certain it isn't the battery (which it isn't if the lights turn on), then it would most likely be the alternator, although it could also be something simple like spark plugs which is extremely easy to replace yourself and don't cost that much either. But it would be best to have an expert look at it!

I would take a solid object and tap the starter a few times, If it doesn't work, than it's most likely the alternator.

Either flat battery, or could be something to do with your spark plugs not firing correctly or your alternator.

I'm having this problem with my Ford Expedition. Already happened twice. So what happened is that I went someplace, got out of my SUV and came back, and it won't turn on. The battery is completely okay, the headlights turn on and everything. When i try to turn it on it makes this sound like it wants to turn on but it gives up. Could it be the alternator? What could the problem be? Much appreciated.