Doby

You certainly have done a very good job of troubleshooting and narrowing down this issue, Because you have tried it with minimal components and swapped ram,video card and psu that would leave only the motherboard or cpu.

Make sure a case speaker is connected and remove the ram and power on, the board should beep, replace the ram and remove the video card, the board should beep.

If you receive no beeps this is a indication that the motherboard is bad but I would remove the cpu and check for any signs of damage