LG G3 hard reset using key combination
How to unlock LG G3 D850 LG F400 forgotten password, remove knock code

If your phone does not restore to its original condition, use a Hard Reset (Factory Reset)
to initialize it.
1 Turn the power off.
2 Press and hold the Power/Lock key + Volume Down key on the back of the phone.
3 Release the Power/Lock Key only when the LG logo is displayed, then immediately press and hold the Power/Lock Key again.
4 Release all keys when the Factory hard reset screen is displayed.
5 Press the Power/Lock Key to continue or either of the Volume Keys to cancel.
6 Press the Power/Lock Key once more to confi rm or either of the Volume Keys to cancel.
lg g3 hard reset LG F400 unlock password
Unlock lg g3 d855 remove password delete unlock pattern

Resetting LG G3 LG D855 / D850 / LG LS990 LG Sprint F400 / T-mobile D851 / Verizon VS985 / Sprint LS990

LG G3 LG D855 soft reset / reboot your LG G3

When the screen freezes or not responding to screen touch or input: Press and hold the Power key for 10 seconds to reboot it.

or simply remove the battery and after a few seconds reinsert it.
lg g3 battery soft reset

Align the metal contacts on the battery with the contacts inside the battery compartment.

LG G3 Safe mode

Using LG G3 Safe mode
To recover your phone when freezing or malfunctioning.
1 Turn off your phone and reboot. When you see the  logo press and hold the Volume Down key until you see the Home screen.
OR
While the phone is on, press and hold the Power/Lock Key until the Phone options menu is displayed. Then press and hold Power off and tap
OK. Your Home screen will then be displayed with the words "Safe mode" in lower left corner.
2 From the Home screen, tap the Menu Key and tap System settings > General tab > Apps.
3 Tap one of the available tabs at the top of the screen and select the application you wish to uninstall.
4 Tap Uninstall and OK to confirm.
5 After uninstalling the application, turn off and reboot your phone.
NOTE: Safe mode will disable all third party applications you have installed. They will be restored when you reboot your LG G3 Android phone again in normal mode.

You can use LG Phone software update tool to update your LG G3 phone firmware if supported.

OR
You can use LG Mobile Support tool to repair your LG cell phone, after download select menu Customer Support > Recovery Phone (F400, D850, or LS880)

LG G3 Hardware key control mode

If your phone display is damaged or broken, you can answer an incoming call, end a call, or turn off an alarm using the hardware keys.
1. Turn your phone off.
2. Press and hold the Power Key and both Volume keys at the same time for more than 6 seconds to enter the Hardware key control mode.
3. Press the Volume Keys to scroll to the desired option, then press the Power key to confirm.
- Answer a call: Press both Volume Keys at the same time.
- End a call: Press the Power Key during a call.
- Stop an alarm: When an alarm rings, press and hold the Volume Up key or Volume Down key to stop the alarm.

General advice: Before you buy a new cell phone or new tablet, please try the following procedure to repair your device in a software way. First charge your battery, backup your important data if possible and in most cases take out SIM and SD card before doing factory reset. It is impossible to recover your data after doing a hard reset, so online backup is always important. For all of your data, a backup should be done on an external device, hard drive, raid system or media. With or without insurance, if your cell phone lost, damaged or stolen at least your invaluable data is backed up in a safe place. If you are about to sell your phone and you want to wipe your personal data, or if your phone affected with virus you have to do a hard reset. In some cases, you can delete the forgotten password or lock pattern from your device as well. All information is for devices with stock based ROMs. If you are using rooted device, always back up your EFS folder first, containing your IMEI info, etc.! Please also note, that a hard reset operation will not unlock your mobile phone's SIM lock or network lock, but it will remove the unlock pattern, remove the user password or PIN password (NOT the SIM card's 4 digit PIN code). Also note that the firmware version will not be affected in any way, it will not be downgraded, it will remain the same you are using and if you have rooted your device, root privileges remain also unaffected.