The new PC's have 2 on off switches, 1 that you can see and touch, and 1 that is command driven.
In cases like this, resetting the command driven switch is simply opening the PC, pulling the power supply connector from the main board, plugging it back in, and your done.
I hope you haven't disected your entire PC before this. It's a common problem.
ETA: I now see your way past this - but for others out there this is how to fix most of the "won't start after a power event" issues.
Good luck.