I can´t turn on my iphone6. It remains black.

A reset may help. Tap and hold the Home button and the On/Off buttons for approximately 15-20 seconds, until the Apple logo reappears. When the logo appears, release both buttons.

No content is affected by this procedure.

This has probably happened to everyone at some time: You press the POWER button on your iPhone - and nothing happens. Usually, this can be resolved easily. Either your battery has run down, or iOS has "crashed" and needs to be rebooted. On rare occasion the firmware has been corrupted, but let's save that for last. The following steps will usually get your phone working again in a few seconds:

1. Unless you are absolutely certain that there is plenty of charge left on the battery, connect the phone to a wall charger for at least 15 minutes. If it was just a low battery the phone will come on by itself. If it doesn't go to step 2.
2. Hold the HOME and POWER (aka SLEEP) at the same time. An Apple logo should appear in 10 - 20 seconds. Relase both buttons, wait about a minute, and your phone should be back to normal.
3. Occasionally it may be necessary to toggle the Mute switch a couple of times before Step 2. No one is sure why, but sometimes it helps if just holding the 2 buttons doesn't work.

If absolutely nothing happens after step 3. either your phone is broken, your cable is defective, or your charger has failed. Try different chargers and cables to isolate the problem. Or take all of them to an Apple store for diagnosis (make a genius bar appointment before going).

If you get an error message, or you see a picture of a USB plug and iTunes, you will need to restore your phone with iTunes. This, fortunately, is a very rare occurrence.