I have replaced the power supply after checking that it was out.
I can get the hard drive to spin with the new power supply while not having the motherboard plugged in. The only light I get is the amber light by the cmos battery, none of the ones up front. I know it is most likely the mother board but have read that it could be the power on button. I can't figure out how to test that. This is an older model Dimension E310 desktop.