I have recently built a AMD (Athlon II X4 635 2.90GHz skt AM3 box C3) system on a Gigabyte MA-770T-UD3 rev. 1.4 ( http://www.gigabyte.com/products/product-page.aspx?pid=3533 ) and with a Seasonic S12 430 ( http://www.seasonicusa.com/s12.htm ). The problem is that, although all the cables and components are connected properly, the system won't power up. I have checked the PSU on another system and it works, but that system did not use the EPS12V 8p cable or the ATX12V 4pin cable, only the mobo connector. My gigabyte mobo requires a ATX12V 8pin cable but I only have a 4 pin on the Seasonic and the EPS 8 pin. I tried connecting the EPS 8pin and it fits, however, it does not power up. Any suggestions and advice would be welcome.