There's a safety switch on those units so make sure you either have the vac tube on or the shield screwed down.
Edit - I've sucked up wood chips and rocks and bound up mine countless times and never had an issue breaking anything. The only times it won't start is when the safety switch wasn't engaged or the on/off switch isn't contacting properly. You can try exercising your on/off switch, spraying it with contact cleaner or WD-40 and pushing it to "on" hard. You could have a funky switch, either the safety or the on/off. Mine needs to be mashed up hard and really should be replaced. I'm not saying you couldn't have other issues but I'd start with the ignition circuit.