my psp slim has a official fw. i upgrde it using the pandoras battery and the universal unbricker. i choose the 3.71 m33-2 for the fw. When i turn on my psp, only appears on the screen is the time, date and the battery meter and the wallpaper. NO icon appearing on the screen. then it shuts down by itself. need some help. how can i restore it to its original fw.