It sounds like the motor has reached the end of its life. The motors only have a limited life and will start to smell and make noises juts before they stop altogether.
It's worth looking underneath to check for any obvious obstructions (remove the base plate using a coin to turn the tabs for a better look) but otherwise I suspect it's the motor.
Dyson do a full service for £69 which might be worthwhile as that includes replacing the motor if necessary. Have a look on their website for details:http://www.dyson.co.uk/support/help.asp ... =goodasnew
Alternatively you could replace it yourself, but you will need to disassemble most of the machine so only attempt it if you're confident with these things. Again, you can buy a motor direct from Dyson (give them a call as it can't be ordered online) or from several online parts retailers.