MSI DKA790GX MOBO

I built computer recently on MSI DKA790GX mobo, Thermaltake M9 Case, Thermaltake 470W PSU, AMD Phenom X3 8650 CPU, and so on. Connected 24 pin ATX power and 4 pin CPU power cables to mobi, as well as front connectors. But when I push power button comp powers up for a sec and then goes off instantly. What might cause that?