I had the same problem with my DC07 it drove me nuts i couldn't find any plastic pieces on the floor or any reason why my dyson wouldn't stand up but then a friend told me about a site that gives you technical advice on problems with dyson's its called www.sparesaver.com i found it really helpful check it out!
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix vacuum cleaners.