Answer: Congratulations, you bought the laptop from hell. Asus should have recognized that the second time your retailer sent the PC back and replaced it instead of insisting the unit was problem-free. And when it refused, Best Buy should have either pressured the manufacturer to do the right thing, or offered you a new computer.
Why didn’t that happen? Well, that’s the funny thing about PCs like those manufactured by Asus. There are multiple parties who could be responsible, from the operating system developer (Microsoft) to the hardware manufacturer (Asus) and there are warranties and third parties that get involved, in your case, Best Buy.
It’s easy to slip between the cracks.
I don’t know the specifics of your warranty, but I can tell you this: All the way down the line, all of the parties involved have a powerful incentive to keep you from replacing the PC outright. The finger-pointing will continue until one of the parties gives up, and it’s usually the consumer who dumps the non-working laptop and buys a replacement, allowing Asus, Best Buy and Microsoft to keep their money. But that’s not an ideal solution.
From what I can tell, all of your haggling was done in person, so there’s no paper trail. I would have started two sets of correspondence: One with Best Buy, the other with Asus. Get their response in writing and compare one with the other for inconsistencies.
Best Buy will probably send you a form response. If that’s insufficient, try emailing someone at the executive level. Best Buy’s emails follow the firstname.lastname@example.org format. I’m absolutely certain that the company’s executive vice president, Timothy Sheehan, would enjoy hearing about your PC troubles (alas, the company reportedly has no CEO until the new one, Hubert Joly, moves into his corner office next month).
I contacted Best Buy on your behalf. It replaced your laptop with one that works.