Hi Paulus,
I have had exactly the same problem with a Corsair HX620, installed it, powered on the system and after about 30 seconds the system shut down and would not restart again, however, the motherboard light remained on so there seems to be some power just not enough to start the system.
Thought it was my mobo so put my old PSU back in and the PC works fine. I can only put the problem down the the PSU dying as everything with the system is fine. Tried the Corsair several times before RMA'ing it but nothing.... Sent it back now for replacement but I always worry that they will find nothing wrong with it!
James