You'll need flash files and a flashing software. Your phone has a Mediatek (MT6572) chip, so you need SP FlashTool to be able to flash the phone.
- Flash files and flashtool can be found here (Just sign up to the site otherwise you won't be able to get those files).
MTK VCOM drivers here
Unzip the files, go to SP Flashtool folder and run the exe file
Install the drivers.
Open flashtool the click on Scatter-Loading
Browse to the flash files folder
Select the MTxxxx-Android-scatter.txt
Now just uncheck the Preloader field the click on Downloading (Green arrow)
Now connect your phone (power off), drivers should be installed and the flashing process start.
Wait till the end: a big green checkmark should pop up.
Phone flashed and problems gone.
DON'T FLASH THE PRELOADER, YOUR PHONE MAY BE PERMANENTLY BRICKED (No powering on, no charging, no being detected by the computer).