In order to hard reset a LG Viper 4G LTE LS840, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
LG Viper 4G LTE LS840 device will be brought back to the default configuration of a brand new device.
1. First, hold down the Power button until the phone turns off.
2. Next, press the Power + Volume Down buttons for, say, ten seconds.
3. Let go of those buttons when an LG logo shows on screen.
4. Press the Power button twice in order to confirm the process. Voila! Your phone should now reset and restart.