IPhone 4s was really annoying me recently because the screen kept going blank during phone calls where I actually had to access the screen to answer those digital voice menus If you had your iPhone screen go black during a phone call, you already know how annoying this problem can be. It may be due to low battery or other malfunction.
Physical Damage. If you restore your iPhone and still experience a black screen, your phone probably has some physical damage. This can be caused by a variety of factors, including exposure to water, exposure to too much heat or cold, severe scratches, or even accumulated dirt.  Level 1 (0 points). 3 times this week, my IPhone 4 randomly shuts off without me even knowing. I go to use my phone and it's just a black screen. The only way I can turn it back on is if I hold the on/off button and the home screen button at the same time for 10 seconds. Then my phone starts working again normally.  When you rely on your iPhone for business and its screen goes black while you are miles from the nearest Apple Store, don't panic. A black screen can have several different causes, most of which you can troubleshoot.  Your iPhone's iOS controls every aspect of your mobile device, and if this software is out-of-date or otherwise corrupted, it could trigger functionality issues such as an unpredictable black screen. Other software you install, including games and other apps, could affect proper operation and cause issues. Even if you're sure your battery is full, power issues could still be what's causing the black screen. Dirty contacts prevent a good connection between your battery and phone, so even a full battery may appear low if your iPhone can't communicate with it properly. Level 1 (0 points). I have had the similar issue with my iphone 5 on vodaphone network: On two occasions the screen on my iphone 5 (ATT) has gone black. The only response I can get from the home button and power button is for it to take a screen shot of the blackness. This occured most recently while completing a voice call. After a few minutes the phone seems to return to normal.  An unexpected black screen on your iPhone is never a welcome sight, as this indicates a low battery or other malfunction. If you've just charged and are certain you're not low on power, the cause of your dark screen could have more sinister roots. Even if you're sure your battery is full, power issues could still be what's causing the black screen. Dirty contacts prevent a good connection between your battery and phone, so even a full battery may appear low if your iPhone can't communicate with it properly. 1 Let go of the power button and keep on holding the home button. 2  Your iPhone should display a white screen or your computer will prompt you and tell you that your phone is in recovery mode and to perform a hard restore (DFU Mode). 3  In both cases, you should be able to restore the phone with your backed up data. Problem. I was using my iPhone and it unexpectedly shut down, despite it having battery power left. When trying to restart it, the iPhone either shows a black screen or briefly shows the Apple logo and goes black again. Please try again later. My iPhone 4s was really annoying me recently because the screen kept going blank during phone calls where I actually had to access the screen to answer those digital voice menus. If you had your iPhone screen go black during a phone call, you already know how annoying this problem can be. 
http://www.ehow.com/info_8771186_do-iphone-screen-goes-black.html https://discussions.apple.com/thread/3910163?start=0&tstart=0 http://smallbusiness.chron.com/wrong-iphone-screen-goes-black-stays-like-that-76889.html http://classroom.synonym.com/iphone-keep-blacking-out-even-though-battery-full-7388.html https://discussions.apple.com/thread/4609879?start=0&tstart=0 http://classroom.synonym.com/iphone-keep-blacking-out-even-though-battery-full-7388.html http://www.ign.com/wikis/iphone/IPhone_Won't_Turn_On http://www.youtube.com/watch?v=VftzpSQorpY
why does my iphone keep going black