If you are lucky, you may just be out of battery. Just plug it in and let it charge. Once it's charged, press vol down + power both at the same time and hold both until the bootloader comes up. If you get to the bootloader, then you can just put the factory image back on there.
If you are unlucky and you somehow blew away the bootloader, then you are SOL. You will know the bootloader is gone if holding the vol down + power does not boot you into the bootloader (assuming you have charged the device and are sure it is not out of battery).