My anti theft system is blinking and won't allow

Question edited for clarity

Not easy to get to or change according to this.

https://www.justanswer.com/mitsubishi/5693h-crankshaft-position-sensor-located-2003-montero-is-diagram.html

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Test fuel pressure at key on. Next test for spark to plugs. Use "noid" light to test for injector pulse.

Does it have an anti theft alarm system ? Sounds like it is tripping.

Exit vehicle and from the outside, lock and unlock driver's door with key. Try to start vehicle.

Fix your car right away by clicking the link I attached
MITSUBISHI MONTERO SPORT SERVICE REPAIR MANUAL 1999 2000 2001 2002 DOWNLOAD

Sometimes, but not always, you can turn off the anti-theft system by locking and unlocking the drivers door with the key. Usually this happens after a battery has gone dead, such as yours did, and the anti-theft is triggered accidentally by the loss of battery power to it. I usually remove the key from the ignition, shut all the doors, lock the drivers door with the key, then unlock it with the key, and then attempt to start the engine. Often the anti-theft will allow the engine to crank but won't let it start. You could have some other problems but I'd start by trying this first.

possible bad speed sensor, get computer codes

I have had a similar problem with mine. The repair shop is telling me there is oil seeping into the alternator and shorting it out. I am going to soo if I can put some sort of shielding around it to prevent this.

look in the ownes manual, if not look to see if anyone has hidden it in the glove box, a favorite spot, or taped it on the radio, otherwise get all the information on the radio serisl no, production no etc and contact dealership

O'Riellys or Autozone. Many part stores can order manuals for yur vehicles.