So they were visible and now they are not? If so then something has changed. First ensure that the SATA cable connections at each end are firmly connected? As Aitchbee says it could be a power issue so have you tried disconnecting the power to one of them to see if that helps?
Yes I initially thought power issue but have tried connecting them both on the same ribbon as the C drive [which must have power to it] - the ribbon has 3 sata block connectors on it, but no joy.
I've just tried connecting them to a different ribbon coming out of the PSU from the same peripherals & sata connector, no joy.
I've also swapped sata leads, but again, no joy. Puzzled.
The only thing I can think of which has changed before this problem occurred was updating drivers via Iobit, which I did a few days ago. Not sure what drivers it updated, there seemed to be a few which updated. If there was a chipset one would this affect the sata outputs?
With this in mind, I've tried doing a restore, but that's been unsuccessful for some reason.
OK guys, have sorted it, but it comes with a tale of caution. Here's what I did:
I identified a date from sys restore when I'd installed IoBit driver booster, which seemed to be the root cause of my problems, especially as it referenced sata drivers/AHCI controller. Don't know how to insert screenshot here but that's what the driver booster entry says in sys restore.
Normal system restore wouldn't work, but managed to do it successfully via safe-mode. Phew.
Rebooted normally into win 10.
Lo & behold, both drives now appear in win explorer & disk management.
I suspect something dodgy with IoBit driver booster, so if you're reading this, then beware. I've wasted 2 days of my life trying to fathom this.