frozen on reboot.

[12MAC]

My sisters phone was freezing up and turning off by itself so we tried rebooting it and now it is stuck on reboot. And then it shows up a little triangle with an exclamation mark. Anyone know what to do or something. Please help.

 

[rnrover]

Hold down the volume up and power button.
Screen will show information
Use Volume up and down to make selection with power button