Q: ran out of gas, now won't start

Your first attempt at resolving should indeed be to simply add more fuel to the tank. Three more gallons will be sufficient if the problem is low fuel. If the starter motor itself is not functioning (i.e., no engine cranking), then the starter circuit has to be diagnosed. If the starter motor is functioning, but the car is still not starting after you have added sufficient fuel to the tank, you could have a circumstance where the fuel pump overheated because it was run dry. That could cause the pump impeller seal to fail. First, check for the characteristic, but momentary, whirring sound from the in-tank fuel pump at key "on". If no fuel pump operation is detected at key "on", check for battery voltage at the pump wire harness at key "on". If no voltage is detected, that circuit has to be diagnosed all the way back to the battery to find the fault. If there is power to the pump, but no momentary pump operation at key "on", the fuel pump would be condemned and replaced. If the pump does operates, check fuel pressure in fuel rail to confirm that it is operating properly and supplying adequate pressure. If you desire that a certified mechanic resolve this, please request a no start diagnostic and the responding mechanic will get it diagnosed and repaired for you. Please let us know if you have further concerns or questions as we are always here to help you.