[G3 Q&A, Help & Troubleshooting] craincrizzy:
Before I even start just gonna let you know you have to flash the phone back to the stock firmware meaning you will lose anything saved on your phone but this is the only way to get it back functional.

Pre-requirements

1. Stock LG cord that came with phone

2. Desktop computer with USB 2.0 ports (3.0 wouldnt work for me)

3. Disable driver signature enforcement (Depends on OS as to how to do this so just google it. Takes just a few minutes)

*UNPLUG PHONE BEFORE STARTING*

1. Download and install the QDLoader HS-USB Driver here: http://www.androidbrick.com/download/qdloader-hs-usb-driver/

2. Plug your phone in while holding volume up to initiate "Download Mode" and it should now show up under "Ports" as "Qualcomm HS-USB QDLoader 9008"

3. Download and extract this: https://www.drive.google.com/file/d/0B_Hol5T47S-bYjNETmVPZkdWUms/view

4. Now download the stock fimware files (the .zip and .dll files) here: http://downloadandroidfiles.org/directory-php/?Directory=/LG%20G3/Stock%20Files/ATT%20D850

5. Extract the .tot file out of the .zip file and place it and your .dll file on your desktop.

6. Now open (be sure to right click and run as administrator!) BoardDiag which is located in the BoardDiag_V2_9 folder you downloaded in step 3.

7. If you need pictures to follow along with the next few steps go here: http://xdaforums.com/lg-g2/general/tool-unbrick-lg-g2-qualcomm-9008-board-t3072073 and see the Attached Thumbnails at the bottom of the first post.

7. At the bottom under "Image Extraction" place the .tot file in the BIN field and make the DIR wherever you wish the files to be extracted to and then hit "Extract" and wait for process to finish.

8. Now under "Board Diag Test" check the boxes beside "AP check" and "EMMC TEST"

9. In the right column make sure "B2 (MSM8974AC)" is selected in dropdown "AP Chipset"

10. On the "Com Port" dropdown select the COM number your device shows up with in Device Manager.

11. In the "Target Dir" type the destination where you extracted the .tot file to in Step 7.

12. Click "START" and wait for process to finish. If the test passes the AP check and the EMMC TEST then you're good to go. If not then im afraid you have a hard brick and I cant help you there.

13. Uncheck "EMMC TEST" and check "RESTORE BOOT IMG" under "Restore Device"

14. In the dropdown beside "RESTORE BOOT IMG" choose the following in the order typed and hit "START" after choosing each file letting it flash the stock file to your phone: aboot--Backupgpt--boot--dbi--laf--Primarygpt--recovery--rpm--tz--sbl1

15. Your phone should now have the LG logo and underneath that say "Security Error".

16. Unplug your phone and pop your battery out and back in. Now plug your phone in while holding volume up for "Download Mode" and this time it should display the "Firmware Update" screen after a few seconds.

17. Now that you have the Firmware screen this guide will help you get your phone software back up and going (THIS IS WHERE YOU NEED A USB 2.0 PORT): http://www.androidrootz.com/2014/07/how-to-unroot-lg-g3-all-variants.html

Good Luck!!

Imporatant: If the OTA update boot looped your phone like mine DO NOT apply any OTA updates your phone tells you to apply because the same thing will happen again (Trust me I tried it)