Same problem to me, yesterday i upgraded my Nexus 5X from 7.0 to 7.1.1 worked 1-2 hours and i used the phone normaly, i'm not a program or so..just trying to speak in whatsapp got crash or something. If i wanted to open with Power button + volume down today it entered in the menu whatever i chose....didn't opened...but right now it seems doesn't even want to open anymore :| And ...what scare me the most is the idea of losing anything from the phone.( i didn't synced my messages...photos...and i really don't want to lose any of them!!)