Uh-Oh. Sounds like the cheap aftermarket screens might damage something in the iPhone circuitry. I have the same issue - put on a new 'cheap' screen and the phone worked really great for about 2 weeks. All of the sudden today, I have almost no brightness, and no response to brightness slider controls. I suppose it is possible that the new screen (back-light) has actually burned out the driver in whichever chip is responsible for back-light control, which may be a fatal failure. The phone is not very usable as is, except in pitch darkness.