Device won't boot past "Android logo" splash screen

Presently, device will boot past the "Zeki" screen but will hang on the "Android" screen. We've let it sit for more than 60 minutes.

Attempted to do a factory reset.

Physical and online manuals do not address how to do this. Listed technical support has been unhelpful. Attempted at least twelve separate, recommended ways of doing a factory reset using the physical buttons (Pressing multiple combinations of the power button, vol + / vol - / both, and the reset button for varying lengths of time at different times during the reboot process). However, I'm certain I haven't tried every combination of buttons, press durations, and timings.

As a last-ditch effort I'm letting the battery run out in an attempt to make it forget everything, but I don't if that will accomplish anything (or how long that will take--days? weeks?).

Any advice on how to achieve a factory reset for this device, or otherwise restore functionality?