How to open the puls pen?

It is just as other have said in that you have to wiggle and pull and twist the top part of the pen. Essentially grab the bottom part of the pen below the silver ring with your left hand and the top with your right hand and start slowly pulling and working the top part and you should begin to see a bit of distance between the blue case and the silver ring. Just carry on pull, wriggling etc until the blue case is free. I've taken mine apart and had a good look around but to be honest things are so tightly packed inside and the component, cables etc are so small that I don't think there is anything that could be done. In fact removing the casing and refitting it has just made the screen issue worse.