car wont start dont know what it could be?

My aunt has a 1983 533i with 210,000 and she would like me to bring it back to life. Well earlyer this summer we went to go start the car and it wont start. we checked battery, alt, fuel pump, fuel regualator, spark plugs. we cant figure out what it could be. We were going to start looking into maybe injectors but not 100% sure. any help or advise on what the problem could be would be great . Bare with me I am still learning about the BMW's dont know much about them.

Start by determining whether you have fue, spark, and air. Check to see if there is spark at the plug connector when you crank it, then check for fuel. Has the car been sitting for a long time? Maybe bad gas? Injectors can get clogged, its not real difficult to replace them.