I've installed a new SSD as a secondary drive and it has worked for two days. At the moment, I can't see any mention of it in Computer (Windows Explorer) and the BIOS only detects 'Intel Bootloader' when it used to detect the SSD properly.
I can't enable AHCI, my motherboard is an Nforce 680i SLI. I've also tried moving SATA ports.
There is a screenshot below of the disk manager, I believe Disk 2 should be the 120GB Intel X-25M G2 SSD (ignore the 8GB USB):
After Hard Drive Diagnostics (SSD is in SATA 4, ignore the rest):