Motherboard led just light for 3 seconds

[isto]

I installed P7P55D LE, i5 processor, Antec Sonata 380W, DDR3 2Gb memory x 2.
When I try to power the system the power on led on the motherboard is light only for about 3 seconds (or less) and then it turns off. Nothing else happens (fans are not rotating etc). Only thing what happens is the led light on and then off..

I tried ASUS power calculator and without any USB devices the system requires 350W power. My power is 380W so it should run.

Antec Sonata power has only 20 pin connector so I needed to get 20-24 pin adapter to that. Can this cause the problem?

Any idea why the system is not starting? I am frustrated...

 

[isto]

I took all the PCI cards away, put the motherboard on table with cpu and memories.. Still acting same, led lights for few seconds and then total silence. Can the motherboard require more than 380W power????

 

[roonj]

There is an adapter available to provide the 24 pin connection which you need.