This really isn't enough information to diagnose the problem. First thing you want to do is try to start the car. Does the car try to start? If not then you probably lost the alternator and the battery is dead. Or the ground on the battery could have come off. Technically your engine could have seized also, but this is almost never the case.
If it does try to start, then you need to check to see if the engine is getting fuel. Just spray a little ether in the intake and then try to start it again. If the car starts for a second and then dies. Then you probably have a plugged fuel filter, or maybe the fuel lines are frozen.
If that doesn't check out then go to a mechanic. More than likely you have something wrong in the ignition system, which takes some expertise to troubleshoot.
