I have had exactly the same, turns off after 5 seconds but only on high power setting… have new battery and all filters clean, I think it is the temperature sensor inside on the motor… however a fix for me is to cup the output vents in your hand tightly, often just one side of the vent slits is enough, turn on and with a little experiment it should keep running, after about 15 seconds you can remove your cupped hand… I believe it re directs cooler air to the sensor, mine then runs fine for about 20 mins. This is for a DC35 but any similar model should be pretty much the same… hopefully eventually of doing this it will start to be OK by itself… let you know.