Try starting it up in "Safe Mode" and see if it will load. If it does, while you will have limited access, that will also tell you that you have something on the device that needs to be removed. Bad app, virus, malware, etc. If, however, it won't go past it even in "Safe Mode", then you will have to either "Hard Reset" the device, to take it to a tech.
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 it, simply repeat the steps above, and you should see "Safe Mode: OFF" rather than on.