Press the "Sleep/Wake" button again to turn on the iPhone. If the screen remains black and you don't see the red slider, reset the phone. Press and hold both the "Sleep/Wake" and the "Home" buttons at the same time for at least 10 seconds. When you see the Apple screen, release the buttons.
Besides, why is my camera not working on my iPhone?
Sometimes the problem lies in iPhone camera flash that doesn't work. Tap the lightning bolt in the upper left of the screen and make sure the flash is On. Try to restart your iPhone (press and hold the Home and Power/Sleep buttons). Turn on the Flashlight from the Control Center.
Why is my camera saying camera failed?
How to fix 'Camera Failed' on Android: Samsung Galaxy S3 or Samsung Galaxy S4. In many cases, the 'camera failed' error occurs because the Camera app has got itself into a bit of a mess. Scroll down to the Camera app and tap on it. Now tap on Force Stop, then Clear Cache, then Clear Data.