Custom PC Boot help

Hey Guys,

I just finished building my custom PC but I'm having a problem. I installed Windows 7 Ultimate (Works Fine) everything is great apart from this problem. When I cold boot the system after POSTing it turns off before restarting and booting windows normally, sometimes it turns on and off 2 time befor it boots. This only started happening after Windows installed. When I restart it boots normally with no shut offs and it also runs amazing in windows but I'm scared of whats going on.

What I Have Done To Help Fix This,
Test different plug sockets on the wall
checked for hardware failure LED's (None lighting)
No F1 Error prompt appeared
CPU Temp 55 celcius
Reset CMOS Defaults
Let system cool

NO LUCK  

SPECS:
Intel Core i7 2600k
Asus P8P67 Evo B3 Rev Mobo
8GB G-skill Ripjaws X RAM
64GB SSD
1TB HDD
nVidia GeForce GT 440
OCZ 500 Watt PSU
Sony x24 DVD Drive
3 Molex case fans


Please Help Me, I'm scared of breaking my system   Thanks In Advance