Try shutting it down and then starting it up in "Safe Mode". If it will load then, while the access will be limited, it will also let you know the problem is either a bad app, virus, malware, etc. The problem would have to be removed from the device and then restart it and it should work fine.
If, however, it won't even start up in "Safe Mode" then it may well be a hardware issue.
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.