Key switch on 1998 taurus

Is it automatic or manual assuming automatic for the moment
If it is automatic try to start it in ever gear by holding the ignition key all the way on and pulling the selector slowly between the ranges
If the starter catches and engine starts the inhibitor switch needs adjusting if not go to the next step which is for automatic & manuals. bridge the solenoid power wire with the main battery wire.
If this causes it to start with the ignition in the on position then manuals may have a faulty ignition switch automatics may have the inhibitor switch wires disconnected or a faulty ignition switch.
if the solenoid goes click click faulty solenoid or if no starter action happens then the the starter is cactus

I looked at info for your security system, it is starter motor disable. I didn't see 06 ford Taurus in my database, so I looked at 05.
Battery has a full charge and battery connections all good?
We can usually do some tests to see if starter motor will crank the engine, but, if the security is the problem, it still won't start.
You can check for applicable trouble codes? Try a different key?

that could be the ignition swicth when you turn the key to take it out its like a kill swicth to spot the spark plugs working. you might need a new barrel look for the key. just I think.

Launch X431 tools

ignition switch keylock cylinder broken or the rack in the steering column broken.

GM has a known problem with their Ignition Switches, Ignition Cylinders.... That is where I would start. The Hard Turning tells me that it was an internal failure

did your car come equipped with prolock? prolock starter kill can become defective and prevent your car from starting. or it can be your ignition switch. I had a defective ignition switch and the van 's fuel pump would turn on but no start...

Is your dome light coming on? do the power locks work?
Your battery may be dead, or you may have blown a main fuse (under the hood)

Have your alternator tested.Your car will not stay running if the alternator is not producing enough power to keep the battery charged.Also have your battery tested and fully charged.Make sure your cables are in good shape.

HI first does your check engine light come on when you turn the ignition switch on ,second if engine light comes on disconnect tps sensor ,dpf sensor,and fuel pressure sensor see if you got your power to injector and cam sensor power try starting engine whit this sensors disconnected if engine runs ,now try connecting a sensor at a time try to start your engine, if it doesn't you found the sensor that is shorting your circuit, hope this helps you,

It's the ignition switch.You will have to replace it.