First step : good battery ?
Second : Enough air in your tank ?
If yes, check the poppet seal is good and the spring is in place and seated properly.
Remove the velocity adjuster (while out of the marker) and when you put it back in, do it up until it stops (don't overdo it, you might damage the seal) and sweet spot the poppet by backing the adjuster out 1+1/2 turns from snug.
You'll need to chrono providing that sorts the leak.