There are a few things you can try. Have you tried restarting it? Also you could try starting it in "Safe Mode" and see if it will boot up correctly. If it does, then it may well be an app that is the cause.
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.
Also, if you have only had it six months, and not damaged it, then it should be under warranty. You can...