I have a black screen

Ms V, sounds like you are having backlight problems. First, of course, try to restart your phone. Press and hold the Sleep/Wake button for a few seconds until the red "slide to power off" slider appears, and then slide the slider. Press and hold the Sleep/Wake button until the Apple logo appears. If that does not work, try to reset your iPhone. Press and hold the Sleep/Wake button and the Home button together for at least ten seconds, until the Apple logo appears. If that does not work, it may be time to open up the iPhone and take a look at the connectors,making sure they are all properly seated and that none of them are broken or torn. You will have to disassemble your phone using this guide. Check to make sure that No1 connector is properly seated and that there is no corrosion etc. If that looks okay, you may need to replace the LCD. For a really simple explanation, the LCD has the backlight, so think of it as a light bulb. Now, if your backlight will still not work after changing the LCD, you have a bit of a problem. There is a coil and and IC on your logic board that regulate the backlight. The coil is an 2R2 and is soldered onto the board. If that should not work, there is an IC right next to the coil, NTLJF4156NXXG and that is the booster for your light, kind of like the power company:-)Attached image show part of the backlight circuit Start with the LCD and the connector first ;-) Hope this helps, good luck.