Originally Posted by LauraPony
Like hpulley said, this is a variant of both the sleep-of-death and the wake-from-sleep problem. Essentially when your device was asleep, it woke itself up enough to turn on the HOME, MENU, and RETURN lights and then froze. This has happened to me before (but never happens when I switch my Wifi to never sleep). If it gets stuck like this while not plugged in, it will completely drain the battery.
I believe the purpose of the reboot button by the battery is to reset the battery. Like I said previously, it doesn't do a factory reset. You always want to try rebooting in this order: 10ish second hold (like hpulley said) - if that doesn't work then try the back button. If that doesn't work then factory reset is the third recourse.
Check around this forum, people have described how to take off the back panel. It sounds like people almost peel it off though. Also sounds like people have no complaints about getting the back cover back on, so I wouldn't hesitate trying assuming it definitely won't wake up after a 10ish second press of the power button and then a 3ish second press to turn back on.
Remember, this will reset your battery, so you might have to plug it back in after you've hit your button. Perhaps (this would be a guess), while your Vox froze, so too did the battery indicator, so your machine thinks it has power when it really doesn't.
OH my, I will contact Kobo help line and see if anyone is at home there. I hate the idea of taking back off. Many thanks for help to date - Happy New Year