Sounds like your cousin downloaded and installed something on the device they shouldn't have.
If you only did a standard "factory reset" then it may not clear it. First try starting up the device in "Safe Mode" and see if it will load up. Many apps won't load/work, but if the phone loads OK in "Safe Mode" then there is definitely something on the device that shouldn't be and it would have to be removed.
Also, if your cousin rooted the device, that would keep you from being to able to do the reset. Start with the "Safe Mode" and if it works fine, then you need to find out if that is what they did so you can proceed from there.
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.