[SOLVED] PC won't start at all

Hey there guys, I need a little help.

I was going to unplug one of my internal HDDs from the PC. Nothing complicated, done it several times before. I took it out, plugged everything back and then when plugging back the power cord to the psu I noticed a quiet electrical sound (similar to when plugging laptop in) but nothing loud or anything. Then I realized that maybe I didn't turn off the psu switch (I'm not sure about this, because I was sure that it was off, but then, maybe it wasn't).

Now the PC won't start at all. Nothing at all, no fans, no sound, nothing. My first thought was that I killed my psu. But the LED on motherboard signalizing power standby turns green when powered.

Other LEDs on MB (gpu, cpu, etc..) were all on for few minutes after I plugged it all back, but are off now. So my guess is that MB is dead. There was no smell from PSU or anything.
What do you guys think?

Thanks for the replies.


EDIT: Now I unplugged the power cord from the PC and LEDs on MB turned on. I'm confused. I thought it's the MB but doesn't it mean that the MB is ok? PC still won't start at all.