Try disconnecting the drive that's causing the problem, boot to RAID setup (Ctrl+I) and break the array. Reboot, then boot to BIOS, undo the BIOS raid configuration then switch off the system after exiting the BIOS. Connect the third drive, restart, boot to BIOS see if all drives are recognized. If so, then reboot and go to RAID setup and create your new RAID array.
"The great majority of mankind are satisfied with appearances, as though they were realities, and are often more influenced by the things that seem than by those that are." - Niccolo Machiavelli