Just had the same problem and in my case it was that the belt had gone on the brush unit. If the brush unit underneath the vac isn't turning then its probably the same case. Easy to fix, picked up a new belt from B&Q (just under £4 for 2) and then went onto the Vax website where in the support section there is a step by step video on changing the belt. Quite easy to do.
Ants, February 2009