Like many others I too have struggled to remove the switch on a Dyson DC04 to repair a faulty cable. I found some really useful information and photographs at www.clayraku.fsnet.co.uk/Dyson/switch.html
In case I have to repeat the repair I have drilled a small hole in the channel that holds the flexible hose - directly opposite the catch on the switch button - so that I can press on it (with a small screwdriver) to release it. This makes removal really easy.
It strikes me that, done carefully, this would be a good way to remove the button in the first place.
David Johnson, May 2005
