You've checked that: 1. Your battery is fully charged and switched on and 2. That the clearomizer isn't blocked, the next thing to check is the connection to the battery. Now you need to ensure that the battery terminal and end of your clearomizer are clean. Using a cotton bud or clean cloth is recommended. If you've cleaned it and still think there might be a connection issue, try loosening the connection slightly. Over-tightening an e-cigarette can often result in the battery and clearomizer failing to connect properly.