+1 for Gary's answer. I have a DC25 that had the same behavior. I overhauled the power switch mechanism more times than I care to remember without luck. After reading Gary's post, I dug into the angle release mechanism down toward the wheels. I found the switch that is triggered when the vacuum is released from vertical, cleaned the contacts with a small file, and reassembled with a little dialectic grease. On mine, the switch was in the levering mechanism, not in the ball. Everything works great now.