Hello there mgrass90,
It sounds like you are unable to access your HBONow app on the Apple TV. I would verify that this is the process you used to restart the Apple TV, because you may have just been putting it to sleep, rather than actually rebooting it:
How to restart your Apple TV
On your Apple TV, go to Settings > General > Restart.
If your Apple TV doesn't repsond when you try to restart it, hold down the Menu and Down buttons on your Apple Remote for 6 seconds, then release when the indicator light on your Apple TV starts blinking. Or unplug your Apple TV, wait 3 seconds, and plug it back in.
If so then I would reach out to HBO support outlined in this article:
Contact Apple TV content providers
HBO NOW
As a last resort you can also restore your Apple TV with iTunes on your computer:
Restore your Apple TV (2nd and 3rd generation)
Thank you for using Apple Support Communities.