Everyday I would come into the office and the Mac would not start. But everytime I packed it up and took it to apple they would not find a problem.
Bad PSU. Part arrived at 2:20Pm. I had the Imac open and ready and the old part removed. Popped it in and put it back together and it started right up. I am very pleased.
Don't rush off to the repair shop. Post your problem in the ifixit forums and let many heads give you advice. Better than just one head anyway.