Hmm, there could be a few problems going on. Lets try starting by putting the phone in "Safe Mode" and see if it will actually load.
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.