Hi, I finally solved my issue after 4 days of cheking (bios, GPU change, forum reading all over the world lol, etc...). There is no PSU issue in fact it was the position of the card in the GPU slot. Maybe the first thing to be checked. Indeed, I installed the 7970m with 5870M X bracket and try to isloate the card componements which can be in interference with the X bracket. For this reason, the X bracket/card thickness was bigger and the GPU was plug in the slot with a small angle maybe 5° (difficult to see by visual checking). Due to this false positionning in the GPU slot, the lappost was posting from time time. After moving it last time, the gpu probably moved a bit and no post was possible anymore. Finally, I cut the X barcket in 4 part and installed it properly and now it is working without any problem. Now I will check that there is no overheating issue in game but the srew are well tight on the card and there is no reason. I hope it can help!!