Starts but doesn't boot up, shuts down after a few seconds. HELP

Hello guys, so I have a computer that has a strange issue. When I start it, it starts up, the fans start spinning, and after a few secs it all shuts down. I tried replacing the RAM but it wasn't a RAM problem,nor a hard drive one. What is more interestning is that, it starts up without the video cards. Without them the processor fan keeps spinning and everything is ok. But when I plug in the video cards, the problem starts reappearing. What should I do?

5 video cards and all are connected via extenders.