Was it wet when you played? It may be that gunge has gotten inside the on/off button, I found the application of WD40 and constant pressing of the button sorted it out after a few mins.
The boards sometimes need trimmed so that the on /off button does not catch on them. My old one if I grabbed the front grip with the board in to hard switched it's self off. So my tech guy trimmed the board and the gun worked mnt after that.