I believe you can hold the “volume up” button and “power” button simultaneously for five seconds. If done correctly, assuming the phone is charged, from there, you should be able to press volume up and down button to enter the boot menu. Try the “reboot” option to see if the phone is still operational so that you may recover pictures, contacts, etcetera, or continue using the phone. If this fails, go back to the boot menu and try the “update from cache” option. Then, if that fails, try the wipe/reset option. Good luck.