How would I tell if an important system part got fried, or things just aren't plugged in right?

ddr347

Commendable
Dec 30, 2016
1
0
1,510
So, this is my first build, and I'm a bit confused. I got everything plugged in, set up, ready to go, flip the switch... and nothing. Check all the connections, cords, etc. None of the case lights come on, the PSU fan doesn't start, no sounds, nothing.

Now, if I disconnect the PSU from the motherboard, and leave it just plugged into the optical drive, and use the 24-pin tester that came with the PSU, and flip the switch, everything works. But, plug the power supply back into the motherboard and nothing works again.

Am I just missing something, is the motherboard dead, or did I misconnect something?