MB: Intel DH67CF
CPU: i7-S (65w)
Scythe Kozuti CPU cooler
Intel SSD
Corsair Vengeance 16GB DDR3
FSP PowerSupply (PSU) PicoPSU FSP090-5DC19 90W

It doesnt start. The led on the MB is lit, thats all. Dead when on button is pushed.
So, is the PSU broken or under dimensioned?

1) Are you sure your PSU is correctly connected to the mobo? Are you using the 12V ATX connector?

2) Is your start button hooked up correctly?

3) Do you have a conventional PSU to use temporarily in it's place?

Do you have a multimeter? You could try jumpstarting the PicoPSU by shorting the ATX power on connector to a ground connector then measure the voltage on any of the 12, 5 or 3.3V lines. This way you sould see if power was coming out which would exclude the PicoPSU from your investigation.

It works with my regular 500w psu. Ill check it with my multimeter.
Is there a chance that its to small for the setup? Anyone have a clue about the boot peek on a machine like this?

No, it's not to small. But I'm personally not so sure about the quality of the "non-picoPSU" picoPSUs. The quality of the brick is also important. Check the rails with a multimeter.

What happens when you push the power button twice in succession? Push it once, and push it a second time quickly after. If it starts, it has something to do with the startup load not being enough to start the PSU.

I have a VIA C7D embedded platform that does this with a normal 12v Pico PSU with a 102W brick.

This might not work, but imo is worth a shot. In my case i had some issues with picoPSU 150XT and 150W brick, it didnt start when i finished the assembly, but its something weird, like the brick or the psu doesnt have the correct values, unpon mulitple disconnects of the cord to the outlet, it starts, and it works great until i unplug it, and once again i have to do the unpluggin trick for some times until it starts and no issues after, even shutting it down, its just when it gets disconnected.

what brick are you using?