Samsung S4 won't turn on

[AC Question]

When I woke up in the morning my phone was switched off (I always keep it on). So, I switched it on and it automatically started an Android update. Then, it switched itself off again. I then switched it on and it came up with 'Touch Wiz Home' stopped working. I pressed the ok button to clear the screen and the phone switched off again. Now, the phone won't switch on at all.

Any ideas on what has happened to my phone and if it can be sorted?

TIA