quite some time ago I decided to fix up a 486 I had for my brother. I start it up, and no video. So I try removing EVERYTHING (except video card of course). still nothing. remove CPU. nothing (not surprised.) then, out of my infinite wisdom, I decide to try the CPU in a different orientation (where I contrived this idea I wish to know). Of course, I got something this time. SPARKS! YAY! and a little smoke from a little resistor next to the CPU socket. needless to say, I put it back in the original orientation and my problem was not fixed. In this case however it is quite sure to have been the Mobo in the first case, as I know the Video card was good (well actually looking back I don't know if it was good, I haven't tested it since then either, some crappy Cirrus Logic thing. The moral of the story? don't put CPU's in sideways.
alright, perhaps I best get back on track.... I've also had, strangely enough, this problem with a Sound Card. Turns out the BIOS couldn't resolve IRQ's for it or something silly like that and just hung. (I believe the Sound card required PCI 2.1 and the BIOS had PCI 2.0, however, so this is likely a redundant fact