Well I have had a new CPU kill a good motherboard before which in turn killed the old cpu afterwards. I hope this will not be the case with your pc.
Do you have a speaker on the motherboard for beeping errors?
Did you reconnect the power button from the case?
Try shutting off the PSU and pull the cable, then hit the power button a couple of times to discharge the motherboard. Then plug the power cord back in and switch it back on.
Is the memory in the right slot (see users manual for the right slot)?
If the power button does not work, try shorting the pins on the header for the power button, should be in the bottom row, the middle on and the next one on the right.
Oh and check if the power cables on the motherboard are all the way in.
