Hello! Thank you for your question. I will be assisting you today.
I'm sorry about the issue.
1. Can you press & hold the power on/off button on the phone for a few seconds, then select the Power off option to power it off, then turn it back on and check?
2. Can you turn off, then remove the battery from the phone for a couple of minutes, then reinstall the battery, then turn it back on and check?
3. If needed,
4. If needed, download and install the Samsung Kies program and back up your tablet:http://www.samsung.com/us/kies/, then reset the phone: go to Apps->Settings->Backup and Reset->Factory data reset->Reset device->Delete all; if needed, see the video instructions at the website below for another way to reset:https://www.youtube.com/watch?v=nft8HVUc5Y4
Please let me know if you still need help with this. Thank you,