When you are trying to "Hard Reset" your phone yourself, are you making sure you start from the phone being "Off"? Can't do it while it is on. Also, you may want to try starting up the phone in "Safe Mode" and see if it works OK then. If so, you probably have something on the phone you don't want. Malware, virus, bad app, etc.
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"...