Why won't it start?

ill answer for NO ELECTRICAL POWER :
sure and is easy with any DMM meter, got one? any $20 DMM.
my guess;1
engine will not crank
dash lamps out.
head lights out. dead.
post systems of electrical system , all parts that work and those that dont work, and problem is easy.
cleaned battery terminals.
tried borrowed battery that reads, 12.6vdc ? (charged is 12.6)
2012 that is in warranty car.... ?
my guess on 2012
jumping a car, that is battery jump starting.
a battery can short, and no jump start on earth will start shorted battery in car. but does lay down some big sparks, or burns up cheap walmart cables.
if the car will not crank, say just that, my starter motor will not crank
jump started from live running other car.
if true then make sure headlights work , if they dont work fix that first.
HL must always work, even keys in pocket.
best is to put a fully charged battery in the car, jump starting can cause
surges that can damage sensitive electronic$$$, do jumps as a desperate measure,
with a charged battery,
1: Head lights work, no fix that , use voltmeter
2: cranks robustly.
no , wiggle shifter lever, (on A/T cars the park switch blocks cranking) On M/T the clutch blocks cranking.
with any dMM
measure battery voltage before crank and during.
12.6v good. reseted.
cranking.
0 to 10v bad (weak battery or shorted starter motor)
11 and above good. and must crank, if not , starter is bad.
to prove starter is bad, check voltage at starter solenoid coil wire lug.
it must be at 11v cranking , below 8v it chatters, and fails.
if at 0v cranking this lug that means the Key start line is failing.
A/T switch not closes, or bad ignition switch.

wont crank or wont start.??
no car starts , if it cant crank. (unless push starter (M/T magic)
that is not a trans sensor its the PRN switch.
ill answer for, wont CRANK !
it wont crank even with a good battery (charged) or jump started.
1: bad start
2: bad wires to same.
so hot wire the starter small wire, the key start line is tiny.
cranks. , starter good, no crank starter bad or cables bad.
if it cranks hot wired, then the key line is dead.
easy, huh?

Park neutral safety switch maybe be the reason for the no crank ! Try putting the vehicle in park ,then try to crank the engine . Testing the electrical circuit is the best way to trouble shoot this problem , along with do a voltage drop test on the starter circuit ! This will test the battery cables an connections .
Starter Voltage Drop
How to voltage drop test starter motor circuit
Does it have a manual or automatic transmission ? Manual ? clutch switch . Looking at a wiring diagram I also see a starter cut relay !
http://www.bbbind.com/free_tsb.html Free wiring diagrams . Enter vehicle info. year , make , model and engine size . Under system click engine , under subsystem click starting . Then click the search button , then click the blue link ! Check the starter cut relay also . Videos on youtube showing how to test a relay controlled circuit !

Do you get warning lights on the dash ?
If yes, a mechanic would check for voltage at the starter.
The circuit between the key switch and the starter has a neutral or clutch safety switch that could have failed.

many things will cause no start problems could have faulty ignition switch.use test light see if power going to starter if not check ignition fuse to starter.if power going to starter, more likely starter solenoid or starter faulty.if ignition fuse okay and starter and solenoid okay still no start problem could be in the ignition switch or inhibitor switch faulty.code scan for faulty theft security system which will also cause no start conditions.

If it won't crank, check clutch safety switch and cables for the starter.
If it cranks but won't start, you'll need to find out if it is ignition or fuel to know where to look next.

So it's a no crank condition? Do dash lights, gauges, and everything else work when the car won't crank over? If so, buy a cheap $5.00 testlight, and when the car won't crank, pull the small black wire off the starter solenoid. While someone holds the key in start (cranking) position and clutch pedal depressed, see if the black wire has power as it should. (Ground the testlight and just touch the wire's end terminal. If powered, the testlight will light up.) If power there, then the starter solenoid is failing. Toyota starters are very good units, but the solenoid's internal contacts get old and pitted.
If no power at the black wire, then the start circuit from ignition switch to clutch safety switch (on the clutch pedal) to starter relay to starter solenoid will have to be diagnosed. To double-check: take a single battery jumper cable and put it on the positive battery post connection. Put the other end of the jumper cable on the solenoid terminal where black wire was removed. Key can be off. Make sure car is in neutral, brake set. If starter now operates, solenoid is O.K., and it is a problem in the start circuit, -ignition switch, neutral start switch, or in the wiring.
Now find a grounding place for testlight under the dash. When car won't crank, check for power coming out of ignition switch on the black wire with white stripe. This is the start wire for the starter solenoid. Key must be in crank position. Wire shoud be powered-ignition switch is working. If no power, switch is failing. You can do the same for the clutch start switch-it's a simple switch, that when clutch is depressed switch is closed and passes power on from ignition switch to the starter relay (thus allowing power to the starter solenoid). Black wire, red stripe-this is wire from clutch switch to starter relay. When key is in crank, clutch depressed, this wire should be hot.
With me so far? Still haven't found a problem, or any loose connections? Next and last is the starter relay. It is located under dash, close to gas pedal, but under the center console, just forward and left of gear shifter. It can be tested and the wiring diagnosed there, but relays are cheap, so just swap in another and see if that helps.
If you have tried everything, and still no help, you could try a new wire from the relay to the starter solenoid. This is that black wire we started with. Older toyotas sometimes have a problem with degraded wiring not passing enough current to operate the starter

Dead battery. Automatic transmission shifter not in PARK. Manual transmission clutch not pushed in or clutch switch defective. Bad battery cable connections. Bad battery cables. Bad starter relay. Bad starter motor. Faulty ignition switch. Malfunctioning transmission range sensor. Wrong key or unprogrammed key for the vehicle. Faulty PCM. Faulty IPC. Faulty BCM. Engine locked-up due to overheating or running out of oil. Interference from aftermarket equipment like an alarm system or remote start....that's some of the reasons this can happen.

It needs to be properly diagnosed so you do not go broke trying to diagnose it by randomly replacing parts.

try locking your car with the key and unlocking it with the key, leave it for 30 second or so between the locking and unlocking , the car thinks some one has tampered with it

You could be right, a quick test to see if it the switch or starter would be to have someone hold the key in the crank postion with clutch pedal down and see if the small wire at starter has power, if it has power then its not the clutch switch but rather the starter itself. or you can unplug the safty switch and jump the connector and see if it starts, if it does then its the switch if not then it could be the starter, check starter for power as i listed above and if theres power replace the starter. hope this is helpful. good day.