Double check the battery with something else. If it works, then my guess is it's not getting proper connection with the Protank atty. The protank doesn't have a very protruding post at the bottom of the connection, so if the post down in the middle of the connection on your battery has been pushed sliiightly down from other devices, that might be it. Try tightening the atty on the base of the Protank really good. Unless you're afraid about "post-pulling" on your battery, this is also an option (using a flat screw driver to carefully raise the post in the battery).
Last option (or perhaps rather your first option over post-pulling, since post-pulling might be meaningless if you don't get a reaction from this method) is to pull out the little post pin underneath the Protank atty. It has a groove across it and a hole in the middle for the air draw. This is what makes connection with your battery. Use a pair of pliers to pull it out (it sits loosely inside a white rubber insulator, so no worries. You can push it back in if you want to). Let it stay halfway in, then screw the Protank onto the battery. The battery end will push the pin in, leaving a somewhat loose fitting but working connection between the posts. If this works, you know what's causing the problem.
Good luck!
Edit: Don't remove the silicon caps on top of the atomizers. It's there to avoid flooding and gurgle. Don't bother with what's inside the tank until you got it working and you're worried about wicking