1) Disconnect everything apart from essentials, so unplug all headers, have the sysfan plugged in, a single monitor cable to inbuilt graphics, remove all third party GFX, HDD etc.
Absolute bare minimium required to power the board and get it to a state of POST.
2) Once you've done this, take a picture of your mobo, so we can see what you have plugged in and where.
It's even been taken to a PC store and they said it was "faulty".