Hmmm I would try restarting the device in "Safe Mode" and see if it will load. If it does then there is either an app (or apps) and/or software on the device that shouldn't be and is giving you the problems. If this is the case, then you would need to remove them.
To get into "Safe Mode" please do the following.
1. First turn off the phone.
2. Next press and hold "Power" until you see the manufacturers logo on the screen, then release the power button.
3. "Quickly" press "Volume Down" and hold it for few seconds until you see the message "Safe mode: ON" or something similar.
4. If you wanted disable safe mode, simply repeat the steps above, and you should see "Safe Mode: Off" rather than On.