Car just stopped running when i was driving,without warning and now won't start

If it's not turning over at all, nothing happens when the key is turned, no click, try having it jumped. If it starts and dies, then pull the altenator out, bring it to autozone or the like, where they'll test it for free. If it fails, and your battery is more than couple years old, go ahead and replace that, too. If it does nothing when jumped and the altenator is ok, put a socket on the crankshaft with a breaker bar and try to turn the engine, if it doesn;t turn, the engine seized. Otherwise, more testing is needed that would be too much to describe here.