In order to hard reset a Lenovo A800, you should perform the following steps.
Remember! Hard reset will delete all the data on your device; pictures, contacts, messages, apps and more.
Lenovo A800 device will be brought back to the default configuration of a brand new device.
1. Press the Power button until the phone turns off.
2. Press both POWER and VOLUME UP simultaneously. Hold these buttons until a warning appears on screen.
3. Select one of these options: Reset Device, Clear eMMC or Wipe data. Done!