Reboot and Select proper Boot device at start up

[Arganis]

Hey all,
My brothers computer was fine, then he got up this morning and tried to turn it on, got the mobo splash screen, then black screen with "Reboot and Select proper Boot device or Insert Boot Media in selected boot Device and press a key"
i checked the bios and ran a diagnostic from the splash screen, and the HD is not being detected.
so i took the HD over to my house and put it in a USB enclosure, and my computer can see the drive, it has a 900+gb partition a ~100 GB system partition and a HP system restore partition.
i can open the 900+ partition and its got all his progs data etc., but the "system" partition don't have anything in it, though it says like 32gb free of 100gb and the "recovery" partition has a couple 1kb files though it says 10gb free of 30gb or something.
any ideas? i thought maybe the HD had failed but im seeing it on my PC.
bad sata cable maybe?
trying to think if it would be something else before it have him buy a new HD

 

[R_1]

the system partition is not user readable, that is normal. while you have access to the drive download the drive diagnostics from the drives website. run and verify that the drive checks out.
different SATA cable. if no result try a different SATA port.
you could also try the enclosure on his PC. if the enclosure allows it to be seen, more evidence the drive is good.

 

[Arganis]

thanks for the response, after testing the drive on another computer, and some other checks, turns out its the sata port on the mobo, all of them, are dead so yay new computer build montage lol