I upgraded my case and took everything out and rebuilt it again. The pc doesnt start . No fans but the motherboard does power

I did but i cant make out much from it. My red usb slot is free . I did cpu . 1 ram out of 4. Cpu fan. 3 pin to a 4 pin. And i think i connected the hdd properly too . I think the problwm is with those very little ones with 2 pins that go on the edge