When S voice was launched all I would see is the blue screen with mic. When I tapped mic or said "Hi galaxy" nothing would happen. I also noted the 3 dots in upper right corner was no longer there. I went to settings>>application manager >> S Voice:
I pressed clear cache and clear data>>pressed Ok for security message then returned to home screen. Opened S voice and the start screen appeared as if I was starting it for the first time as a new phone.
It's now in working condition again.
Note: use my fix at your own risk. I am no responsible for any lost data or damage to device. What worked for me may not work for you.