My engine will not crank over why?

I had this problem and had to get a starter cost me $134.00

So on Friday I stopped to get gas and when I got back into my car it would not crank. I made sure the gear was in park and tried again and it did crank. On yesterday I pulled off from the redlight and it started to skip per se like twice and then it stopped. Today I stopped to get my mail and when I got back in my car it would not crank. WHat could be the problem. The batter is fine. The car just had an oil change on Friday. It has one half tank of gas in it. Could it be the transmission?

Car sat about 3 months started up fine run and died had battery recharged took out srarter had it tested and fine hooked up starter put battery in connected pos tryed to connect neg car was turning over without key in car

Engine Mechanical problem
2003 Pontiac Grand Prix 6 cyl Front Wheel Drive Automatic 166000 killometers

tried to start my car last night sounded like it was going to turn over but wouldnt start, tried this several times but eventually the starter noise stopped and it would just "click" when attempting to turn over. Jump started it and it turned over and started. But was hesitant. Turned off after letting it idol for a bit, restarted it and it started but was hesitant again, few hour later tried it and it started but again was hesitant. This morning went to try to start it and no start again, again will at 1st sound like it will turn over but eventually wont even turn over, just click. Please help! Was told may be battery, started, selinoid or alternator?

Thanks for your prompt response to my inquiry, I will check these out tonight,

but I also wanted to mention that the lights, radio, heat everything works when I turn my key over. Even after it doesnt crank anymore and just clicks.

Also sometimes when I start my car it will idle up & down a few times before idle'n normal. And a few months ago my check engine light came on I took to the dealer$hip & they said something about wanting to do a smoke test to determine if there is a problem, with a seal or valve leaking? I dont know exactly. But they reset the check engine light & it hasnt come back on.
I didnt know if this would also be a factor to the same problem i'm having with it not starting?

Thanks!

When I try to crank the car, it doesn't turn over and makes a loud clicking noise, kind of like a dead battery but not like one I've ever heard. So I install a new starter and that doesn't work. So I lean towards the battery or alternator. I replace the old battery with a brand new one and that didn't make a difference either. Now I'm stuck and out of ideas.

@CJ MEDEVAC: I am almost positive that it is the anti theft system. But I am not sure where to look or where to start or what to look for to fix this problem. I had issues with it a while back with the security. Supposedly, I was using the wrong key and it locked down. Lol. After weighing out all my options, I figured that's gotta be what it is! So. What should I do to get started on this Anti-Theft Project!
@madmike1732: I will give this a try but I'm pretty sure the engine isnt seized because when I try to crank it, I can clearly see (it lift and go back to starting position) the pulley move. So I figured if the engine had shut down, then none of that would move at all. Right!

Please help I have a 2000 grand prix and when I go to start it will turn over but it will not stay running unless I keep my foot on the gas as soon as I let off it dies my friend looked at it and he said it might be the idle air control but we replaced that and and its still doing the same thing

It hasnt been on