If your suction is ok for normal cleaning and bad for just the hand tools then you have a blockage in the flexible hose or the "u pipe" at the bottom of the flexible hose. Un-clip the u pipe and check it for blockage. Un-clip the hose from the vacuum and you should be able to look through it when letting it hang straight down.
Hose removal here
http://www.youtube.com/watch?v=NfZlHIFlwJc
.
some options for this are craigslist, search >dyson>broken>vaccuum>DC 07
Options 2> we used duck tape for a year and it worked fine, then when a broken DC07 was posted on craigslist we bought it for parts.
The most likely problem is something was not put back together properly in the clutch. You can move the belts by hand with the clutch out of the machine. Move the motor belt and switch the lever off and on and see if the brush belt is turning on and off. It not you will need to take the clutch apart and reassemble it. Test it before installing.
If you visit
http://www.sparesaver.com/help-and-support/dyson-section/dyson-technical-advice-450/
they have alot of info on repairing dyson cleaners AND they sell the
parts, cheapest ive seen online.
Check the cord first to make sure you are getting power to the switch. If not replace the cord, if so test the switch to make sure you are getting power through the switch. If still not solved follow the power down to the motor and make sure you're getting power to the motor. If so and still wont' run test the motor.
Sounds like it might be a moisture issue (one of the causes that will not allow the vacuum to function fully) IF you ran the vac over a wet part of the floor (like I did, too soon after I had shampooed a carpet) OR had cleaned/washed/rinsed the HEPA-prefilters and they had not dried completely. If whatever part of the vac's system "see's or senses" moisture, it WILL fault and not let the bar operate. Sounds silly hearing something like that, but I think the same reason is pointed out in the owners manual. IF this is not the cause, I might lean toward a overload condition pertaining to the bar mechanism, like something binding the bar or in the drive assembly. Hope this helps in some way!