Samsung Galaxy S4 won't turn on and it is HOT to the touch. What should I do?

[AC Question]

Was on the charger all night, as per usual. Picked it up this morning to check it; it was at 100% per usual, so unplugged it; checked for messages or missed calls and set it down. Picked it up several hours later as I was headed out and it's off; can't turn it on.

 

[belodion]

Heat suggests that it needs repairer attention, and fairly urgently. Back up your stuff now while you still can.
It may simply need a new battery, so check that first.