suddenly phone turn off and cant be open anymore

i was swiping the screen to find the app i wanted to open but suddenly my phone screen turned black. i pressed on the lock button, but nothing happened. then i removed n inserted the battery, the phone vibrated and the screen shows Samsung S4 Gt-19505 for a second, then the screen went black again. i have also tried to charge my phone, but nothing appear on the screen. how can i solve it? because i have some important sch work saved in NOTE.

i didnt drop my phone on the floor or into the water before.what have happened to my phone?

Thank you