Hood release cable is broken or loose. How can hood be opened?
Try using pliers to pull on the hood release cable. While holding the outer cable. In the mean time a second person should be pushing down on the hood. As you keep the cable pulled, the person at the front of the hood can try to jiggle the hood and hope it releases.
If this method does not work you will have to access the hood latch release either through the grill or from under the front bumper.