Is your tank leaking or gargling?
If you get a gargling or bubbling feeling or sound when you inhale, it could be that the coil has taken on too much liquid ad become flooded. You can fix this by holding your device by the battery and giving it a couple of short, sharp flicks downward. This will remove the excess vape liquid or e-juice from the inside of the coil.
If your tank is leaking, first make sure that the coil is screwed down fully and isn't cross-threaded, that all seals are in place, and that the main part of the tank and the base ase screwed together fully, but only finger-tight because you may stop the tank coming apart later on.
Also, your tank starts leaking right after you've fixed it, it could be that it was overfilled a little, but the leak should stop after you've given the tank some use..
However, if none of these tips fix your leak, simply change the coil out for a fresh one as an old coil can start to get a bit leaky!
Is your tank not producing any vapour?
If you're not getting any vapour from your vape tank, check the tank on a spare battery if you have one as this will confirm that the issue is with the tank and not your battery.
Then make sure that the coil in your tank is inserted properly and has been screwed all the way down. Also check that your tank is screwed onto your battery correctly.
If this doesn't solve the issue, then simply change the coil out for a fresh one.