the power led doesnt even have to be pluged in ...
i test mb's with a switch and a speaker ussually ...
were did you get the mb ??? sometimes places like new egg or other online outlets will resell a rma'ed part .. (someone elses screw up .. or bad component .)
If its a new mb id would say try to float it
(take out the back panel were the ps2,lan,ect connectors are then slip the antistat plastic bag under it , leaving the screws out .) carefully hook everything up and try to boot it .
listen for the "post beep"
you can also hook up one conponent at a time this way also for troubleshooting
now if the main power cable atx connector is missing a pin then theres something wrong ...
some led light connections have split pins (AE pin space pin )
also double check the jumpers on the board and beshure they are set properly .