I don't think anything happened, but the thought that I might had forgotten to unplug the power chord before fiddling with MB screws left me feeling stupid. Is is possible to short circuit the mb by doing that? I was just checking if I had tightened them too hard.. if anything has been damaged i would know in general right?
As long as the pc and PSU aren't on. If the PC is off but the PSU is on, the PSU is still supplying some voltage to the motherboard. It's possible to damage a pc when it's off. But the best way to know if you did do damage is to see if it boots and behaves normally.