My pc off and on itself when I power on

i am using vs 550 watt power supply wen i turn on my pc its on and off itself again on 3-5 sec. after and running smoothly.i ma using

Gigabyte h61m-ds2,

Intel g630 processor 2.7Ghz.,

4+2 ddr3 1600 mhz,

Sapphire hd 7770 2gb vapor-x,

160gb+1tb+1tb+EX500gb hdds,

Circle 830 cabinet with 5 fans

USB 3.0 PCI card ,

Corsair 550 smps,

Canon LBP 2900B additional cartridge,

Canon lide120 scanner,

D-LINK DIR 600 L,

2.0 Lenovo multimedia speakers,

Deepcooler Frostwin V2. cooler

LG DVD-R/W

Microsoft lifecam vx-1000,

Apc600v ups,pagaria

automatic voltage stabilizer

Intex 19" TFT monitor,

Marvo km400 combo multi color,

5050 RGB with IR Remote still upgrading....