HI, I'm reading your problem,
Let me explain something about your car.
2005 Ford Taurus, The key on that car has Chip inside of the key and receiver on the ignition switch,
Check if the key you are trying to use is Black and has a plastic head.
If not you need a key with that characteristics.
But if you have the right key, Remenber if you had drop on the floor, or hit with something,
Because some times they come damaged, with insignificat thins.
Remenber if you left the key close to a magnets like speakers.
If nothing aply at your case, you need to call a place Aloha Smith, they have the computer to program or reprogarm your key. IF not you can't start your car.
OK.. I hope this information work for you.
Thank's for submit yous question on fixya.com
You might have cut a wire or it could have broken or disconnected. Try tracing the wiring where you hooked up the trailer you may find one broken or disconnected.
At one point the door was lock from the in side and then closed and then unlocked with alarm, try un-locking it from the drivers door, then from the in side push the un-lock button and then close the drivers door. U should have no problems with it, but they do say that putting the key in the ignition and then do what you would like starting it but don't and do it 2 times and then start it will tell the alarm that it is not stolen.
Do u know that key less entry code to your drivers door?
Let me know if you would like your code that is if you don't know where to look.
Try disconnecting the battery for a couple of minutes so the electrical system reboots itself with a clean start. That might fix it. IU would give it 10 to 15 minutes disconnected before reconnecting and trying it. Further to that i would say take it to the dealer and send the bill to the place that did your oil change
Either the starter is bad, or the starter solenoid.
Under the engine, between the rear of the engine and the front of the transmission. It will be on a mount with an oil cooler, (it has metal fins) on the driver's side.