Do you hear any beeps?
What light on the Frount Pannel & MB come on?
Recheck that all the connectors are plugged in firmly.
ok...may sound dumb, but just to be sure, check that you still have the power cord plugged in and that it is turned on at the wall and back on PC.
Make sure that the main power connector is plugged in firmly to the MB, then then press the power button and check if the Fan on the PS is working?
Also, do the CD Drives open & close?
no beeps no lights on the MB and for front panel im not sure lemme check.