Problem Solved -
All the clues I mentioned were misleading. It turned out that the computer required a momentary closure of the power switch to start. Well, the power switch was sticking, maintaining the start signal. That is what was causing the cycling I described. The Antec case is overall nice for the price but the Power and Reset switches are cheap and flimsy. I'll add a touch of lubricant which should remedy the problem..
Great to see it is solved. Yes correct with the switch if keeping contact it will recycle after a few seconds.