will turn over but will not crank
Your question doesn't give much information to work with. But most of the time when this problem arises suddenly, it's a dead or dying battery; you might have enough juice to light the lights, but not enough to get the engine started. Jump start the car properly; leave donor hooked up long enough to charge your battery, at least ten minutes. If your car starts, fine. If it does not start, replace your battery. After either of these, go to an auto parts store and have any codes read. They may point you to the reason your battery died. If it's none of these, there are many things that can cause a car not to start, both electrical and fuel related. Only a mechanic who can actually see the car can find the cause.