Have you tried holding the Volume Down button & then pressing the Power on button (while holding the VOL Down?)
Can you boot into SAFE MODE ?
- Press & hold BOTH vol up & down buttons at same time
- Power up the phone - continue to hold the vol buttons for like 1-2 mins ..
If successful, should come up saying "SAFE MODE" in lower left corner. Does THIS work? Power off & on as usual then. What happens?