Yes you are absolutely right although there is no reason they could not determin wether it's a bad motherboard or not through a simple process or elimenation... It's either a faulty motherbooard or a faulty part connected to it... Assuming that the motherboard is at fault and cannot be reset.
ITs fixed new mobo owns! and they computer guys are cool! and know what they talking about trust me! lol! but its true i my dell broke down 2 and they said what ya expect how you think they build a comp witha 17'' screen for 400$ crap parts lol! but mine aint 400$... i am rambling.... anyways just me taking out the memory and testing and putting back screwed the whole thing! so now i am using that with a new mobo! the cases are made to only accpet dell mobos! whats up with that? the guy also had to resoder the whoel front panel and so other stuff to make it fit. they say they have even seen power supply connectors backwards so it only works on mobo like insteadt of being 12v it be 4v and so on... anyways i appreciate you sticking with me on this!
And of course anyone could do this with any motherboard on the market if not done right for example static electricity and such. And even the top company's are not perfect and will have a bad product or two.
Anyhow I'm happy you got your computer working and are happy with it!
I just realized somthing that brings me back to the guys being full O sheet..
Did they suggest that your testing the memory did this as you suggested? because you didn't even do that until you already had the problem so this is not possible.
If you read back you'll realize what I mean
As a matter of fact you mention there was no problem until you set somthing with cool and quiet I believe And it was later suggested by myself that perhaps you test your memory in case of a bad stick which was a desperate reach if anything because even with a bad stick of ram you should be able to enter your bios ..