I replaced the mains flex on a dysaon upright recently (sorry can't recall the model) and was a sod to get into.
I eventually figured out you had to remove the on/off button to locate a screw underneath then the switch and flex assembly could be lifted out. The button was held on with a plastic clip on the button and the idea was to push a very thin instrument down the side to release the clip nearest the handle and lift off the button (don't be surprised if the clip breaks as it did with me as the araldite came in handy).
sparky
November 2005