first of all, take out you battery wait 10 seconds Press the power button for 45 second the install the battery. 2- if the first method didn't work try to enter download mode like this: turn off your phone, connect your phone to your computer then hold volume down and home button

1. Take out your device's battery and wait for 10 seconds. Press the power button for 45 seconds and then install the battery.

2. If the first method didn't work, try to enter "Download mode" like this:

• Turn off your phone;
• Connect your phone to your computer and then hold Volume Down and Home button.