sounds like you lost and output on your power supply. if all the outputs are not there or at the right voltage..no post. I would start with the simple stuff first. make sure all the header connectors are connected right. on the mb and on the case side. a lot of times it the power on cable falls off the daughter card on the case or the on switch is bad. if the cable looks fine then i would look into seeing if there a short somewhere. I would pull the gpu and all but one stick of ram and any extra cards. see if the mb comes on. if not i would try a test power supply with the system bare bones and see if it posts. with it bare bones you may want to try and clear the cmos and see if it does anything. if this is a new build and a first post issue do you have another cpu?? the mb needs to have bios 815 or higher to post with your new cpu. if it was working fine then died then you have a bad part somewhere.