On a normal boot-up, the CPU fan will go into high rpms for about two seconds and then go to lower rpm, the keyboard lights will flash, then the display will come out of stand-by, displaying the splash logo and start-up options. Since none of that is happening, I wonder if it's a BIOS problem, but I have absolutely no idea how to even check that, let alone fix it.
To eliminate other hardware from the suspect list, I've swapped out (one at a time, of course) the power supply, HDD, and CD/DVD drives, display, and keyboard - and they all work fine when mounted in another system (the one I'm posting this with). There is still no change in my son's system when new PS, HDD, etc., from this system are installed in his system. I also tried to use an emergency boot CD. The light on the CD drive flashed for a few seconds and the disc spun up, but nothing else happened after that.
I've tried everything I know of and I'm stumped. I would greatly appreciate any help in figuring this out.