91 Chevy Cavalier wont start.. any ideas?

[Amanda E]

My dad is a mechanic but sometimes I don't trust him completely lol I have a 91 Chevy Cavalier and so far it has been amazing and I haven't had any problems with it until recently. One day out of the blue it wouldn't start. My battery is fine, lights came on perfectly but it won't turn over. I have never had problems with it starting before. My dad said it could be one of two things (the second one I forgot =/) but the first one was a sensor in my ignition? I wish I could give you guys more information but I am mechanically impaired lol