My Optimus G is stuck in "Secure Booting Error! Cause : boot certification verify" and I can't seem to do anything at all. When I hold down the power button the screen turns off for a couple of seconds and then it turns back on and displays the same error. It's almost like the device isn't turned off but rather is locked and I can turn it back on using the volume buttons instead of the power button. I've tried to hold down the volume up and power button bit nothing happens so I can't connect to it through my computer and I'm unable to get it to boot into anything.
Is there anything I can do to revert it back into stock?
Specs: LG Optimus G E975 International
Edit: I'm also unable to power off the device.