this is the one i have
http://www.metrix.net/images/RB:433%20ROUTERBOARD.jpg

when i power it by POE it turn on few seconds then after 10 seconds it turn off by itself , no light nothing.
but if i power it to the DC connector it stays on and works fine.
it is brand new.
any ideas why is it happening?

Check LED on POE injector, in some case when you connect RB it goes off together with RB.

i found the problem , i had the two mini pci cards were tosted , they dont work.
i put new ones and now everything works fine.
thank you everybody