In the brief window between obtaining the phone and rooting it, I noticed my battery tended to get hot. Since root with custom kernel that problem has gone away.
Unlikely, but worst case scenario you fried your battery. Batteries and heat are mortal enemies.
As someone else asked: stock charger? Third party / cheapo chargers can draw more current than they are supposed to which might damage your battery.
Try connecting via stock usb cable and computer; this is a less rapid rate of charge. Once connected, try to turn on phone. If successful, unplug and see if phone stays on.