We could try the fun obvious solutions:
- Reset BIOS to factory default, either by taking out the CMOS battery or through BIOS itself
- Make sure the SATA ports are configured to look for drives
- Change the ports the drives are in
- Change the cables
- Hook up the drives in another computer or use a USB<->SATA dongle
- Make sure if there are jumper settings, that it's configured correctly
Thanks for the quick reply LatiosXT:
In the BIOS there is an option under Advanced Setup, SATA configuration for SATA inputs to set as Hot Plug but all are disabled (although I don't think this has anything to do with this). Strangely enough, I just restarted the PC and entered the BIOS again and voila; one of the HDDs appeared! Still not the other one. I made some other changes to the BIOS, specifically the CPU overclocking, but again I don't think this has anything to do with my problem. Will go on to boot into Win to check if the one HDD that just popped up in BIOS is present in Win.
I will follow your advice and change ports, change cables and check on another computer as last resort.
Any other comments/ideas welcomed!