If the phone is not allowing you to do anything, then you have to factory reset it. Factory reset will delete everything from the phone and install a fresh working software on it. If you want to factory reset it, then follow the steps below (remember, this will delete everything from it and restore it to factory condition);
Turn off the phone
Press and hold down Volume Up + Home + Power buttons at the same time for a few seconds.
Android system recovery will be loaded now
Select wipe data/factory reset. (Volume buttons to go up or down, select with Power button)
Select Yes — delete all user data.(Volume buttons to go up or down, select with Power button)
Then select reboot system now(Volume buttons to go up or down, select with Power button)
That should factory reset the phone. Then setup the phone again. Please let me know if that didn't work, so we can continue troubleshooting.