Question Added an extra HDD - now all my drives are gone

Nov 30, 2018
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Hello,
I've been building my first PC for a year now, and having just taken on a new short film decided to expand my HDD space and bought a secondhand WD Black 1TB.
I popped it in the remaining HDD slot, hooked up power, connected the SATA cable I'd already put into the MSI Gaming Pro Carbon X370 SATA 6 slot as it was behind my graphics card, so I pre-planned that one, booted up and...
No OS detected.
Launched BIOS - it detected the USB drives, SATA 4 (my old 500GB HDD) but neither SATA 1, my SSD (Samsung 500gb) with OS, nor SATA 6.
Disconnected all but the SSD, rebooted. Still not detected. Switched cables around. Nothing. Switched which port the SSD was connected to. Nothing. Even put SSD into SATA4 with the cable that was working with the small HDD. Nada.
Checked Advanced setup, can only enable or disable HotPlug, all SATA ports say device not present.
Flashed BIOS to most recent. Still nothing.
I was supposed to be having a viewing with my director today so this isn't great timing.....

Edit: FFS, I think I had a loose powercable. But now my CPU LED is on. Resetting BIOS and let's start from scratch.....
Edit2: back to functioning monitors/BIOS/CPU but still no SSD
Edit3: rejigged the power cables from coming through the closest hole to a top one and using the middle male into the SSD and we're alive. Still no new HDD though, but the others are back
Edit4: Fixed! Apparently I shouldn't use the males for tidiness but flexibility. Or the SATA cables need bigger gaps between males. Using 1 & 3 not 1&2 and HDD is online.