Carputer problem

Hi guys im new here so sorry if iv posted in the wrong section.

Basicaly my problem is this,
iv just built a carputer and my car psu came today.....wired it all up and plugged it in to turn it on a install windows but when it turned on the led on the motherboard stays on but the led on the psu keeps flashing on and off like its not getting a constant power. The motherboard fan comes on and goes off with this flashing led aswel. So its almost like its turning on and off within a couple of seconds and i am stumped as to what to do next.

So any help would be great.
Cheers guys