Phone shows no display but it gets hot

Hello guys,im new to this forum and i have a question,so today my HTC Desire 820 Dual Sim got out of battery and put it on charge,after the light turned green(fully charged) i took it and wanted to open it,i heard all the sounds and vibrations of the phone,it even got hot but i still dont see anything,i havent tried rooting it or anything else...and by the way if it cant be fixed will it be repaired by the warranty ?