Aspire Nautilus Tank is a kind of adjustable airflow tank, which can be a bit of a learning curve. There are a lot of factors involved.

First your juice. If you are vaping high VG ratio juice, you may need to move the airflow to the smallest hole (tightest draw). This will allow the wick and coils to pull more juice. Otherwise, if you have it on the largest hole (lightest draw) you may not be creating much of a vacuum to draw the juice onto the wicks.

Secondly, your draw. If you have a very light draw you may be causing the same issue as with the lack of airflow. There isn't enough of a suction to pull juice through to the wicks / coils.

Thirdly, your maintenance. If you recently cleaned it out and filled the tank, you may need to wait a little time for the juice to flow through.

Fourthly your device. If you have a variable volt / wattage device, you may have the voltage set too high.

Fifth, your coil. It is possible that the coil or the wick is burnt or blown.