Hate to say it, but it could be a lot of things. Are you using a thick
juice (high vg, etc)? Did you give it a few mins to wick the juice to the coil? I use EVODs, which have the same head as the protank 2, and I have a few juices I'm still trying to get to flow right. There are a lot of threads out there that talk about removing the "flavor wicks". I haven't had to do that yet, usually I just change my
vaping (draw intensity, wait between puffs, etc) to make sure I get the right vape. For 80% of the juices I've tried, though, they work like a champ.
Another thought, did you charge the batt and are you getting a good connection? I've had issues with some tanks/batteries and solid connections.