If you relate to the phenomenon of a black screen with a flashing blue LED notification also, then you must perform your following key combination to restart the device:
Power On / Off Button
Volume - Button
Hold the key combination so pressed until the flashing blue LED is off and the smartphone reboots. You see this very rapidly at the boot screen of Android on your Samsung Galaxy S6 Edge. Subsequently, the smartphone should be used as usual.
You know now, what to do when the Samsung Galaxy S6 Edge only displays a black screen and a blinking blue LED.