Check to see if the camera will operate when removed from the hard wire, if the camera operates then check the hard wire connections and that the light on the regulator operates when the ignition is on.
If the camera will not power up, please format the SD card as corrupt data and stop the power up sequence.
If the camera powers up the turns off, check that the SD card is not full if you are not using loop mode. Double check that the camera is set to loop mode if using it. If not, format the SD card.
Look to see if the USB port has been damaged on the back of the camera.