Computer Wont Start

I opened my case today and wanted to connect another motherboard to the my current powersupply. The motherboard ended up being defective and I connected the power cable from the powersupply back to the motherboard. When I press the power button on my computer nothing happneds. I opened up the case and I tried doing the same thing, I see the fan spin for one second and I see the a little light come on for one second and then everything turns off. When I pluged in the speakers I heard a littel chirp. I unpluged the powercable from the motherboard and pluged it back in, the computer does the same thing, it turns on for one second and turns off. I have checked the cable from the button to the motherboard and it is fine. I also replaced the power cable from powersupply to the wall, still didnt fix the problem. Thanks in advance. Any help is appresiated.