Dyson DC07 belt keeps snapping?

Hi there.
We recently got a 10 year old dc07 (standard) from a friend, as it wasn't working and they decided just to buy a new one.
When 1st looking at it we discovered the belt had snapped and therefore thought this was the main problem. We also noticed the small clear pipe was a bit cracked. So we ordered some parts(genuine) and replaced them. We also gave the dyson a good clean up.
Within the first 5 mins of using it the new belt had snapped exactly like the old one. Before it snapped it appeared that the brush was turning fine as the dyson was picking up fine and the suction was great. It was obviouse something was wrong when the belt snapped as it made a rather nasty noise and smoke came out the bottom, and I had to turn it off. At no point did the motor cut out.It appears the belt snapped at the end where it is attached to the pin. We have checked that the brush rolls easily and are at a bit of a loss as to what is wrong.....Can anyone help?
Thanks
K & J