If it is the same as mine (model SHT 24-2), you undo all the small screws you can see. The grey mouded bit on the top of the handle unclips if you ease a small flas screwdriver along one edge.Then there is another screw under that.
Remove the blades and motor/gearbox. Theer are 3 small screws and 2 large screws holding the bottom plate on, remove these.
In there is a small gear and the large wheel that makes both the blades move in and out.
I bet you will find the same as me - the two prongs of one of the blades that the large wheel pushes and pulls the blade in and out is broken and jammed.
Anyone know where I can get new blades for this model? Searched the Net, its well out of warranty.
Ray
November 2007