Ton, I had a similar problem with a Cube yesterday. The Cube is always lit up from the StudioDisplay button. When I removed the Studio Display I could not get the Cube to start, unless I removed the core. The fault was that there is a black washer about 25mm dia combined with a white disc, and this combined object had become misplaced (I suspect the previous owner!) I replaced it - quite complicated, I had to take the Cube casing apart - now it works fine - no cost at all! I cannot be sure that this is your problem, but it sounds like a possibility. Best wishes, David.