First off, Welcome.
Second off, I am not overly familiar with the I-Stick (Other than what it is, but I don't actually own one). I know some in the forum have said that they have to press fairly hard on the fire button to get it to fire but you sound like you're not firing at all.
If I had to speculate, I would guess that it's a bad coil or perhaps a pin that's gotten moved out of place.
However, trust me, one of the experts (we have so many around here) will see this and can give you a good trouble shooting guide, hopefully soon! Because it's no fun having a non functioning vape pen. Been there, done that . . .