You can try booting the phone in "Safe Mode" and see if it will load. If the problem is a bad app, virus, malware, etc., it should allow you to bypass it by going into "Safe Mode". However after that, you would need to remove whatever is the cause before you could boot out of "Safe Mode".
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.