When I hold down the power button at the top, it does not give me the option to shut off, restart, etc.
Is the phone powering off or is the screen just turning off?
I know exactly what you're talking about because its happened to me twice. I don't know why/how but I found on a forum how to fix it:
Go to Settings, click Security. Then make sure there is a check mark in the Secure Credentials box.
