After looking at lots of videos on the internet, I took 5-6 hours of my time, doing very carefully my computer.
At first, the test build I made outside the case worked perfectly.
But when I putted everything inside the box, plugged everything, the power wouldn't turn on.
Seems like the power-supply was dead.
I ordered another one, and I shipped that one back.
Today, I received that power-supply. I plugged only the 20+4 pins in the motherboard, and everything was fine.
After that, I plugged everything in my computer (fans, hdd, video card, etc). I turned on the computer, and everything worked perfectly!
So I looked for my Windows 7 CD, I putted it in the dvd-burner, turned back to do something quick, and when I looked back at my computer, it was turned off. I pressed the power button, and nothing happened.
Sometimes, when I press the power button, the fans would work for maybe half a second and then dead nothing.
So I'd like to know, if it is possible that i'm unlucky enough to get 2 dead power-supply in a row, or if maybe something else is going wrong in my computer, or if I did something wrong, or if something in my build is incompatible or something..
Thanks in advance, and sorry about the quality of my english, i speak french most of the time.