Alright, so here's the situation.
I have in my possession a Dell Optiplex GX280, that won't power on. It has the amber blinking light when the PSU is plugged in. Now at first, it seemed like the motherboard, because we took out/unplugged each individual part till it was only the motherboard, cpu, front usb/power port (which contains the power on switch) and the power supply. So we ordered a new Mobo in.
New mobo comes, and we still have the same problem. Tried replacement PSU, and CPU (though I can't guarantee that the other CPU was compatible with this board, or working). The one oddity that I have noticed now, is that if I unplug the front usb/power port and plug in the PSU with just the mobo/cpu the fans starting kicking and the machine seems to power up. Though I have no video display what-so-ever. Tried a known good video card, and the same issue. It's only when I have the front usb/power port plugged in that the computer won't power up.
There are also no error codes displayed on the front panel. I've looked around at similar situations and unfortunately haven't found one that helps my current situation. Does anyone have a clue what could be causing this?