Press and hold your power key for a slow count of up to two minutes to see if the phone will power down.  If this does not work, please remove the battery, wait 30 seconds and reinsert the battery and attempt to power the device on.  If this does not work, please contact the Sonim Customer Experience Center at 1-833-MY-SONIM (1-833-697-6646).  We are open 24 hours a day, Monday-Friday.