It can happen that you need to press against the battery door while trying to move the latch with your fingernail. If juice leaked into the battery door, use a bit of vodka to unstuck the latch by gently keep wiggling the latch back and forth... don't apply brute force because the latch is spring loaded and these little springs can break. As for why the mod stopped firing. First thing is always to check your batteries if you haven't already. Could be something as simple as the adjustable 510 pin on the mod needs re-adjustment, but always measure the ohms of your atomizer before jumping to any fast conclusions, and, even then, you can't be sure so what you need to do is, disassemble the mod and carefully inspect every little detail, properly, before putting the mod properly back together again. Familiarize yourself with the mechanics of the mod. It's the only way to avoid unpleasant surprises.