What is the likely thing that goes when a motherboard dies?

[Gustavus]

I know it isn't feasible -- at least for me -- to repair a motherboard, so this question is just to satisfy my curiousity. My favorite system was based on an ABIT IC7 G motherboard running a Prescott P4. rock stable, not overheating, and able to run Prime95 indefinitely without errors. The graphics card was an older ATI Radeon 9600 so when I had a chance to pick up a Radeon X1600 with 512 M memory I did. On booting up the system reported new hardware found etc. but once the drivers were installed it worked beautifully. Ran it for several hours before turning it off. When I started it the next time it did not go into the boot screen and the monitor showed no signal. The new video card is the problem I thought, so I switched back to the older Radeon that had worked for many moons. Same thing -- no boot and no post audio. I have a good lab, so I swapped another CPU (known good) same thing. I pulled the memory and ran memtest on another machine in the lab -- no errors no matter how long I let it run. I have numerous power supplies, so swapped a supply -- same thing. I then opened a brand new OCZ power supply -- still the same. If I pull the RAM modules, I get the long audio beep as I should. The fans all run, the LEDs on the motherboard all light, the drives power up etc. Given that the memory is good, the PS is good and the CPU is good that leaves only the MB. I have looked it over very carefully and then are no obviously bad capacitors, burnt components etc.

Not that there is anything that can be done to fix the problem, I was wondering if any of you know what it is that typically fails on a motherboard. I am sure there is no visible indication of what failed, but just out of curiousity I would like to know what (probably) happened.

Thanks

Note added
Yes I cleared CMOS -- several times

 

[mpilchfamily]

There is no typical fail. You can have a number of problems. First of which could be bad capacitors on the board. Check all the caps. If any are buldging at the top or bottom its bad. I've had an old S478 board that took a surge on the system that damaged the BIOS chip. You could even have a damaged chipset.

 

[Gustavus]

mpilchfamily,
Thanks for the reply.

I am pretty sure it isn't a capacitor -- at least not visibly. I have been a tech since the 1940's when I was a radar tech in the Air Corps/Air Force so have a lot of experience in looking for visible failures in electronic assemblies. There is a place in Holland that advertises BIOS chips which is about the only thing easily replaced on the motherboard. Do you think it a worthwhile gamble to replace it -- just on the chance that is what failed?
Seems like a bad gamble to me -- just wonder what you think.

 

[mpilchfamily]

My pas experiance has been that a BIOS replacment chip cost nearly as much as a new motherboard does. So its not really worth it. Also you have to weigh that cost. There is a good chance the chip replacement won't work so now your stuck with a chip you can't use and your out that money that could have gawn to a new board. So i agree its not really worth it.

Tax season is uppon us so this may or may not be a good time to consider a new build. Or just replace the board.