No power chevy express 1500 van wont start

Hi there, if you turn on the lights do you have head lights? if yes turn the key to start with headlights on does the lights dim? Yes? if yes that means your key is operating the starter if not it means the starter is not receiving a signal from the key to starter, need to know what it does before I go on. If no lights then the battery is dead or you have a corroded battery cable. Let me know for more information.