Ok, I have an ECS k7s5a mobo with an XP1800+ stuck in it and it's dead. The RAM works in two other PC's and the PSU powers up those boxes just fine. This mobo became glitchy and very quickly failed to display even the video card information during POST. The video card is currently in another PC and working fine. I have tried clearing the CMOS leaving the battery in and taking it out, and leaving it out for a week. The fan that came with the cpu never failed and in fact blows more air/spins faster than either of the fans that came with the two XP2600+ cpus so it's chilling one of those boxes. The question: since I suspect the mobo or cpu is it safer to try another working cpu in this suspect mobo or should I drop this cpu in another mobo? Thanks for helping me not let the smoke out of the wrong part
I have the same basic setup you do, so I guess I can comment. First off, don't be surprised that the mobo has gone down 'in flames'. This is my third K7S5A and none of them has working onboard sound, even though that was a listed feature on the box and the connectors are on the backplane. It's just a totally crappy mobo and if someone out there has a perfectly working one, it's as close to a miracle as most will ever see.
Now, as to your particular problem, I'd say go the whole mile. You've tested everything except the CPU and you seem to have access to other, known-good systems, take the CPU and try it in another box. If that works (as I expect it to) then take that piece of crap mobo (unless it's under warantee) and toss it in the trash. Then turn around and get a good one. Shouldn't be too expensive to get an equivalent replacement these days. I'm not ever going to buy another ECS board, though!