Why won't my iphone 5s work?

So i was facetiming my friend, and then my phone just blacked out. It didn't offer me to shut down it didn't do anything, it just crashed. I tried clicking the home button, i tried clicking the shut down button, i tried putting it on silent and off silent, i tried adjusting the volume but it is not doing anything AT ALL. The only thing it has done is it said "sorry the connection is poor please try again later" or something like that. It did that twice. This phone is pretty new, i only got it in january, which was like 5 months ago, and it doesn't have any cracks in it, and i never dropped it in water, i don't know what going on help!

Added (1). like a voice verbally said sorry connection is poor please try again there was no message on the phone the screen was compeltely black it verbally said that

Plug in the charger and wait a few minutes for it to get enough juice to boot up.