I'm not quite sure what you are wanting to know. If it's how to get those boards booting again, you could start with the Intel Website Troubleshooting system boot issues page.
If you are wanting guidance on how to change soldered on components on motherboards, generally that's specialist work so should not be attempted by people without the required specialist equipment and training. I've worked as a computer technician and the only time I've ever performed such a task was on my home server to change a damaged serial port socket (which wasn't stopping the board from booting by the way). The hardest part of that job was obtaining the exact correct replacement part - the desoldering/removal and soldering on the new socket was a breeze by comparison!
If all the components are OK on a motherboard, it follows that the motherboard is not the cause of the PCs failure to boot. The most common part to fail on PCs (aside from fans) is the PSU so maybe those defective PCs need testing with known good PSUs? Does that answer your question Sam?