Try starting up in "Safe Mode" and see if it will load. If it does, you have either an app, virus, or malware on the phone that is going to need to be uninstalled/removed for you to start it up correctly. I would start with any apps or other files you added recently.
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.