If you didn't jailbreak iPhone and not intentionally trying to change the lighting in other ways, the high probability, your iPhone has broken and needs repair in service center.
As a rule, there are a few reasons:
1. Faulty chip backlight, resulting in no backlights on iPhone 4s and 4. Most often, it suffers from any liquid or shock. In order to backlight once again worked in this case, you will need to replace the chip.
2. One of the most common situations when the liquid reaches the jack of screen, as a result, burn connector in place, where the tracks to backlight. If this is the reason why the lights are not working iPhone 3g and 3gs do this, then the replacement of components is not necessary. The tracks will be easy to restore.
3. Faulty display. Despite the fact that the lights not working iPhone 3g and 3gs for this reason it is not so often, yet not be ruled out that possibility.
And yet, if the iPhone does not work lights, and the image is, to continue further operation becomes quite difficult, because there is a feeling as if the brightness of the display just reduced. Go for help in service center, and no matter what your iPhone. Will it be 4s, 4, 4g, or known enough models, called 3g, 3gs, 2g.
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