Are you still struggling with this? It is best to provide links to what you've done (i.e. which ROM you flashed before your issue was created, "stock kernels", "updated miui rom", and "PG86IMG.zip").
All of those things are ambiguous, and are not clearly defined.
The problem is that you've most likely tried to flash ROMs that require S-OFF, and you
definitely shouldn't be flashing anything named PG86IMG.zip with S-ON.
That said, I have a guide that will help you. You'll need to get into the bootloader (pull the phone's battery out, plug your phone into the computer with the USB cable, replace the battery, wait for the red light to come on, press and hold the volume-down button, and then press the power button). For the things you're trying to flash you want (need) S-OFF.
My guide will get you there. Follow every step to the letter, including the preliminary steps. If you have problems with the instructions, post your problems there.