Computer powers on, then turns off within seconds

Hello, I've been using this computer for a good 5 months and it had been working well. During this time, I had a loose 24 pin but it still worked. One day, when I kicked my computer accidently, the 24 pin came off and my computer turned off. Ever since, I couldn't fix my computer, it would turn on and then off. The fans would spin then stop spinning. I've tried forcing the 24 pin in but that did not work. I also tried the paperclip test and my psu fan was spinning.
So later, I took out my psu, graphic card, hard drive, and ram out and replaced it in my old computer, next thing you know it worked perfectly. So I suspected that it was my mobo that didn't work propely so I used my warranty to get a new one. Today, I got my new mobo and set everything up, but I still got the same problem. What seems to be the problem ...?
I have a ASROCK Z97 Pro4 motherboard and my psu is the evga supernova 550 gs.
Please help, thank you !