My Evo 3D does that. I have to reformat it. Hope you have insurance because it may be a deep problem if reformatting it does not help.
You can reboot the phone using the Android system recovery.
If you are still having issues here are the steps for a factory wipe on the device, this WILL DELETE ALL YOUR DATA on your phone and set it back to a factory state.
It turns on but doesn't get past the Sprint screen before it shuts it self off and does the same thing over and over again. I actually have to take the battery out in order for it to turn off.