Has my mobo gone?

[Gingerbread Man]

Computer used to work just fine. Then it went through a phase of not turning on correctly, well it had power, fans in their ready state, low RPM, but it never went to POST.
Now the power button does nothing. I believed it to be the PSU. Just put a new one in, nothing. No change. Power button does nothing.

I have tried bridging the cable out, the jumpers on the motherboard for the power button. Nothing.

Next step I believe is the motherboard? I don't think it's RAM or graphics etc as it's not evening posting, it's doing nothing. Dead.

Am I right in my prognosis? Any other steps?

D