I will describe a few simple steps to perform a hard reset on the Lenovo P780:
1) Turn off the device if it is on.
2) Press three buttons simultaneously: volume up, volume down and power button, hold until recovery mode appears.
3) In the menu, pressing the volume buttons highlight the item “Wipe data / Factory reset” and select it by pressing the power button.
4) When the cleaning is completed, select the “reboot system now” item in the menu, after which the device will reboot.