Is the car turning over or not. IF it is the battery, you will either get nothing when you turn the key, or maybe a clinking sound, or a very slow turn over for a second or two. IF it turns the engine over and it doesn't start, then it might be a fuel problem. Or, if it turns the engine over for some time then starts, it might be a fuel problem...need more information...
If you get nothing or the clicking sound, try cleaning the battery posts first...