96 cavalier turns over won't start

my daughters car was running fine until she left it out overnight in -40C without the block heater plugged in. AMA came to try and start it three times over a couple of days, then towed it to my son's home where it has been in a garage(thinking everything may have been frozen). Gas line anti freeze was added. Car will turn over, but will not start. When ignition is on the anti theft light is constant. we have tried the leaving key on and waiting to see if it is the anti theft, but it didn't work.

Any suggestions would be appreciated.

I have a couple of ???s 4 u car batteries usually don't like cold weather.. and you were right in wanting to thaw out the car.. one was the battery checked?? does it have @ least 12.5 volts ..if not you'll need to charge the battery (ideal would be w/ battery @ 70 deg f. at two amps for about 10-12 hours) this will give the battery a good charge.. I would also disconnect the battery from the car and reconnect besure not to have the key in the ignition and all lights and acc. offf..