2007 Mazda CX-7 died while driving, won't restart.

alieneila

I was driving for about 5 hours, then on the highway the engine just shut off. When I checked the oil, it was out so I walked to the store and put 5 qts in. I was hoping a safety sensor had triggered the engine to shut off. When I turn the ignition, the engine turns and whines but there isn't any fire. One guy who stopped said the relay was fried and that the starter is bad. Another guy said if the relay was fried the battery would be dead and if it was the starter the engine wouldn't be spinning. So at this point I'm completely lost. Any ideas?