Hello. If you have an automatic, take out the 4 bolts around the axle... I learned this the hard way. Take off the 4 bolts and the entire part mysteriously comes right out.
Buying a used engine in always a risk. I have a hard time shelling out the money for one, especially when the mileage is unknown. To me its always been a toss up to rebuild or just buy a used motor, I cant make up my decision! good luck!
Have you checked the basic's? I would check to make sure your timing belt is still together then make sure your electrical system is charging properly.
Turning the key in the driver door lock should do the trick, If all else fails, remove the alarm. Its not like you even have a remote key fob for it. Best of luck. Alarms are funny sometimes.