You either have a battery that has a dead cell and needs replacing or something is on pulling power from the battery. Can be any light on the vehicle or a stuck relay. In rare instances a defective alternator can cause this.
check ignition switch and efi relay
Call OnStar
The hood should still open when the battery is dead
By inserting the key in the door lock and turning.
dead battery or starter
Key
Just pull the hood release inside the car. Use your key to unlock the door.
Then either something is on draining the battery or the battery has a dead cell draining all the rest and must be replaced.
I would use my key
Use door key on door
Dead battery? Battery cables in need of cleaning or replacement?
A dead cell in the battery or something is on, such as the headlights. A stuck relay will also cause this. More likely than not, the battery has a dead cell and needs replacing.