I had this same issue last week. I dropped it in water, briefly, and it worked for another 4hrs or so. Then it tried to do the Marshmallow system update, but failed to ever turn back on after. Verizon told me how to check for water damage, and there ended up not being any. You need to take a pin of some sort to get the sim card out of the phone, and then check to see if there is pink color inside of the area - if so, there's water damage.
Thank you for your reply.
I removed the sim card and saw No discoloration at all, however the phone still will not work. We have had to go through Verizon to get a new phone, unfortunately, as nothing works to get it working again.
Again, Thank you for replying to my inquiry.