The power “switch” is a sliding lever that engages a microswitch (which does the actual switching). However the design of this is so %#*@ dumb as to make one despair for the state of the human intellect. If this happens again, get a small hammer, slide to the “on” position then give the body a sharp love tap right above the speed control dial. If it then comes to life you’re a victim of bad design. If you look at the picture of the dremel 4000 electrical assembly replacement picture earlier in the thread you’ll see a black box on the left. That’s a microswitch. The blue plastic “on/off” switch we humans operate is nothing more than a long strip of plastic that reaches all the way back to press this microswitch. The trigger on the microswitch is nicely rounded so that something sliding over (and travelling down the long length of the component) can easily operate the trigger. However, in the dremel the microswitch is mounted sideways so the blue plastic on/off lever (which is soft plastic) has to scrape up...