My Nexus 5 was turning off randomly, and today it turned off completely (80% battery). I couldn't turn on, it didn't respond. I connected it to the cable and it began a Google bootlop, showing it for about 1 second and then showing it again. I'm not pressing any button and the bootlop persists. I cannot enter the recovery mode, it resets with 2 seconds or less. What do I do?