It sounds like the motor has overheated and has now been irrepairable damaged.
The motor has a built in over-current trip to protect itself (and you if it seriously overheated and caught fire). This normally automatically resets itself, however if the motor has just about had it, the moment it is switched on, it just trips again.
The primary cause of motors overheating is that the filters are not cleaned or replaced frequently enough. Dont be fooled by Dyson's "lifetime filters". They need to be regularly cleaned and replaced when necessary.
Replacement motors are avaible on eBay for about £25, however repalcing one requires good DIY skills and tools.
Have a look at
www.dysonmedic.com and see if you feel you can tackle it yourself. If not, take it to a repair shop or call the Dyson helpline.