If you can get into download mode by holding Vol Up and then connecting a USB cable (while the device is off) then this method will work for you.
Thank you @rwilco12 for hosting the download
1. Download the above Zip and extract it to a folder on your Desktop called "LG G2 Stock" (or whatever you prefer to name it).
2. Install LGUnitedMobileDriver from "LG G2 Stock" Folder
3. Install Setup_LGFlashTool from "LG G2 Stock" Folder (You will get a log in error if you try to open it)
4. Extract MegaLock.zip from the "LG G2 Stock" Folder to C:\LG\LGFlashTool and overwrite existing MegaLock.dll file. This gets around the Log in Error you got before when you tried to open it.
6. Put phone in Download mode by holding Volume up for a couple seconds and then plugging the phone in via USB.
7. Go to Windows Start Menu and under "search programs and files" type "device manager" and open it up.
8. Go to Ports (COM & LPT). You should see LGE AndroidNet etc... Right click it and go to Properties > Port Settings > Advanced > Change COM Port Number to COM41 > OK > OK > Close Device Manager
9. You should have a LGFlashTool shortcut on your desktop. Double Click it to open it up.
10. In the Model Config that opens up Select Manual Mode in top left.
11. For DLL browse to "LG G2 Stock" folder and select LGLS980_20130904_LGFLASHv151.dll file
12. For S/W browse to "LG G2 Stock" Folder and select LS980ZV7_01.tot file
13. Hit OK and then click the Yellow Arrow in top left of LG Flash Tool. Wait for it to say "READY!!"
14. Unplug your phone and power it off (it may reboot before you can power it off).
15. Go back into download mode and the stock ROM will start flashing on it's own. It should take no more than 10 minutes. It may stop around 80% but your phone will say 100% and reboot and Presto! Back to stock or unbricked! (Whichever you were trying to do)
Thanks and I hope this helps!