Hi. Sounds very much like the motor has expired. The contacts wear out when they get old so it will need replacing. If you're a reasonably confident DIYer it's a pretty easy job. You can pick up a new motor off ebay or one of many Dyson part suppliers. They start at about £20. Alternatively you can just replace the contacts but I've never tried that. Fpr £20 I'd just buy a new motor.
Here's a guide on how to do it:
http://www.dysonmedic.com/DC07%20Folder/DC07%20Motor%20change.html