As Flux said, if you already have a few days on it, toss it.
If relatively new, try this.
- Remove from the battery device. Turn it upside down, with drip tip facing the floor. Be sure the wick holes of the carto are in the air space of the tank. With a paper towel on the connector end, blow relatively forcefully through the drip tip. If you get some decent air flow, that's a good sign. If not, the carto is probably unrepairable.
- Next put the cartotank back onto the battery device. Turn your voltage up to around 5.5 volts (if you have a regulated PV). Do some short pulse dry burns of a couple seconds in length. No more than a few. Then attempt a gentle draw with power on.
If these two methods don't work to salvage the carto, nothing else will that I am aware of.