EliteBook 840 G2 keeps losing the internal drive — “No boot found” and DST shows “Not Installed,”

[Karteltech1]

I’m running into a strange and frustrating pattern with the EliteBook 840 G2, and I’ve now seen it on four other units owned by friends. Everything works fine until one random restart or wake from hibernation, then suddenly the laptop throws “No boot device found.” When you open the HP BIOS diagnostics, both the short and long DST tests instantly say “Not Installed,” as if no drive exists.

The odd part is that nothing is wrong with the drives themselves. Pull the same SSD or HDD out, put it in an external USB enclosure, and it reads perfectly every single time. Other laptops also recognize the drive immediately, so the storage isn’t failing. Yet once you return it to the 840 G2, the system acts like the bay is empty.

After seeing the same behaviour across multiple machines, it really feels like something inside this model — the internal SATA path, ribbon, or connector  just gives up with age. No errors, no warning, just a disappearing act that makes the BIOS think nothing is installed at all.

I’m posting this to find anyone who has run into this exact issue and actually solved it. Not guesses, not “try a different drive,” but someone who fixed this disappearing-drive behaviour on the 840 G2. What ended up being the cause? And what finally worked?