Why is my vape pen on but not hitting?

Excuse me, I'm having some issues with my vape pen and I was wondering if you could assist me. It seems to be turned on, but it's not producing any vapor when I inhale. Could it be a problem with the battery, the atomizer, or perhaps the e-liquid? I've already tried cleaning it and checking the connections, but it's still not working properly. Do you have any suggestions on how I can troubleshoot and fix this issue?