if it is the kbox mini, it should be same mod that comes with subox mini kit - check your firing pin (brass colored pin at bottom of 510 connection where you connect tank to mod) - it may have gotten pushed down, you can try using a very small screwdriver (flathead) to pry it up gently, working around edges (and make sure mod is off, so you dont accidentally press firing button while doing this)... great little mods, but the fixed pin is somewhat notorious for getting pushed down, depending on what type of tank you are using (i generally only use mine with the kanger subtank/ subtank mini)... other connection checks as suggested by suprtruckr are a good idea also