Why is the Action Center on my HTC 8X not working?

[Windows Central Question]

I've got a Verizon-branded HTC 8X with Windows Phone v. 8.1 Update installed. The action center won't slide open to view notifications, etc. I've tried a hard reset several times, including reinstalling firmware using the Windows Device Recovery software. I just bought this phone, used, and the Action Center has never worked. All other phone functions seem fine. This phone has not yet been activated. Any suggestions appreciated.