Returning it for repair could be the best thing ever but it's a second hand tablet and the warranty has already passed. I've even tried to reset it using the small pinhole provided but nothing happened. Seems that the firmware is stuck in some kind of boot loop.
No worry for now cause microphone is still ok (y).
It seems that there's a universal solution with the wm8650. I'm going to check it out since for "pisoi" it seemed to have worked.
I'll come back later on with some good news hopefully...