Alright, I just recently tried to build a computer out of spare parts. After assembling it, it ran buggy for a while and then died with a fried electronics smell. After disassembly, I found that the CPU fan I had installed on it was improperly built; the fan had been attached to the heatsink upside-down, making it unable to turn. So I wrote off the processor, and possibly the motherboard, as roasted.
I then got another motherboard/processor combo, which I know works, and connected the power supply to it. It failed to start. I know the power supply works, because up until yesterday, it was powering my Athlon XP2000+ system. The 'working' motherboard is a GA-5ammc with an AMD 400Mhz K6-2. The only things that are connected to this motherboard that are from the previous, destroyed computer are the hard drive and the monitor, and the case. Video and everything else is onboard.
The most response I can get is a flash of the keyboard scroll-lock LEDs if I set the MB jumper to enable keyboard power on. Note this flash happens when I turn the power supply on, not when I press the soft-power switch on the front of the case. It doesn't boot to bios, make any kind of beeps, flash the monitor, or turn on the fan. I've used a continuity tester to check the motherboard to see if it has current - it does - and am all out of ideas.