Rooting the LG G3?

So my brother has a LG G3 on Sprint and it broke during a system update today. He has know way to truly boot into android and his phone isn’t rooted. We took the phone to Sprint and they said it would take them four days to fix which is outrageous! So my solution to this problem is to try and root the phone without booting into android, in hopes of installing CyanogenMod. The problem is, is that I can’t find a guide anywhere on to root the phone when you have no access to android. Can you all please help me find a way to root this phone so I can get it up and running again.

Tried flashing the stock firmware? http://forum.xda-developers.com/showthread.php?t=2785089

No I haven't would this fix the phone if done correctly?

Can you by any chance get into download mode. If so look for a guide to flash back to stock. They generally use download mode and don't require root or access to Android or even recovery (or at least on my g2).

Assuming you can get into download mode and its not completely borken, it should. If not youll likely have to send it away, I dont know of a way to flash a new recovery without access to the OS.

edit: your plan would be flash stock > root > flash twrp recovery > flash any rom you want.

Once you have twrp installed, your phones pretty much always recoverable

Awesome I will check and see if I can get into download mode in a few minutes and let you all know how it goes.

Yes I am able to access download mode on the phone.

Root phone = warranty is void. So choose carefully.
You should be able to flash whatever compatible ROM you like via a usb cable + odin or other methods.
roms - http://lgg3root.com/

I'm going to try flashing it back to stock firmware and see if that fixes it first but if not I'll give it a try, thanks for the suggestion.

Although that applies to @LinuxForYou, just for anyone else reading, this does not apply in the EU.

@Eden Thank you so much for the help I got my brothers phone working again.

Awesome. Got twrp on it?