Rob Hi,
Not sure if your problem is that there is no power to your machine (i.e. you press the button and nothing happens) or the cable is totally damaged, if its the first please read below;
I have had the power go twice now on my DC04 - the first time I paid to get it fixed (doh)...but the second time I decided to have a go and fix it myself, if you look where the power button is, it is surrounded by moulded plastic(grey, if yours is the purple/green model), now this is the tricky bit, you need to carefully lever this off, it WILL break the grey plastic but it (that you can put back afterwards)should come off in one piece, once this is off you will be able to see what is under the button, you should be able to see a torque head screw holding the button in place, remove this screw using a torque head driver and then look at what the cable is doing, my guess is that the connector has come loose, simply push this back on and put everything back - I think this is caused by standing on the cable when using the machine (great design feature huh!!)
I hope this helps, cracked plastic is worth it, better than paying the repair dude cash anyhow.
Matty, August 2005