My G750 suffered a bluescreen a couple of months back, after which the SSD in the left drive bay failed to register. I've tried a few different drives and they all register in the right bay, but do not show up at BIOS in the left one*. The physical connector is not at fault, I have replaced the SATA sub-assembly on the small ribbon cable without effect. I am currently working around the issue by connecting my second drive through a DVD tray caddy.
* Left and right as viewed from the front in normal use.
During my repair attempt, I noticed an unused ribbon connector on the motherboard labelled SSD. I'm wondering if I could connect the drive bays to this with an alternative SATA sub-assembly.