Interesting SATA HDD issue

[Piersonrife]

This question may have been asked somewhere else, but I have an interesting issue with one of my co-workers computer.

The computer is an Asus CM6870, that seems stock, except it's been upgraded to Windows 10 and the HDD says that it's SATA 3, but Asus' web site shows that the drive is (supposed to be) a SATA 2. She brought it to me because it wasn't booting past BIOS. Suspecting a possible failed HDD, I cloned my system drive (to have a HDD that I could instal to see if the system boots), and installed it into her computer - using her existing HDD connections and cables. Her computer saw my HDD and booted without any issues. I connected her drive back, and the computer would not boot. I installed mine on a different header, and the computer booted, but did not see her drive. I told her that her hard drive was toast. Fast forward a few days - her computer is still here, waiting for a new drive - and I decied to tinker with it a little more. I installed her HDD into my computer to see if mine would recognize it ... and it is seen and accessable in Windows. I am currently doing a virus scan on her drive.

This makes me question if she has a faulty HDD or not.

To try to recap -
HDD not seen on native computer.
Cloned HDD is seen, and boots, on both native HDD cables and header, as well as separate cable and header
HDD IS accessable in different machine

Any ideas?

 

[Piersonrife]

To update - although I'm still confused as to what is going on - I used my computer to scan for viruses ... aside from a few PUPs, it came back clean. I ran a "self test" (using my computer) on the drive, and got no errors. I re-installed the drive to the original machine, and the computer boots up fine, at least to the log in screen. Since I do not have the pass code (nor do I really care about that information), I can not get past there. I'm still stumped, though, as to why her computer initially refused to see the drive when I was working on it last week. Any ideas? I'd like to be able to tell her something, other than "I don't know why it wouldn't work, but it's working now". Is this an indication that something could be failing, or something that could be fixed with a BIOS update or something. Some specs that could help out is

Intel i7 3770 processor,
16GB ADATA RAM
4GB of RAMAXEL RAM
A 1TB Sata 3 (6GB/s) Toshiba HDD
all connected to an ASUS P8H77-M Pro motherboard,
AND POWERED BY A aC bEL hba008-za1gt 300 WATT psu

The BIOS version is 0708