Thanks for your replies.
The 90w is probably more suitable for a much lower wattage cpu.
I guess it's possible, but others are running very similar systems from 80W PSU's which don't pass the 12V straight through. http://www.silentpcreview.com/forums/viewtopic.php?f=23&t=62704&p=546062&hilit=g620#p546062
Is the DC-DC board plugged in correctly, it's only 20 pin the mainboard connector 24 pin?
Have you tried with minimal components, only the mainboard and ssd attached?
The (old) standard ATX PSU that i'm using temporarily only has a 20 pin connector and this works with no problems. The motherboard manual also specifies that it will work with only 20pins.
I've tried getting it to post with nothing but the 1 stick of ram and the case plugged in. The case uses 1 1/2 internal usb headers and i'm not sure what this would draw... i'll check once more without these plugged in.
I have been in touch with LinITX since my first post and they have (very quickly I must add) replied with the comments below asking me to return the picoPSU and brick.
It is possible that this board and PSU combination does not work properly.We have seen occasional problems with startup timing. Alternatively there could be a fault in the PSU. It would be best for us to test the PSU.
I shall try the picoPSU without the case USB's attached and then return the kit to LinITX for testing... If/when I resolve the issue I shall post back, but if anyone else has a possible explanation please feel free to share.