Morit,
I don't believe a BIOS upgrade is needed, or will resolve. Have you confirmed correct BIOS settings for the controllers operate mode?
Obviously RAID, needs to be RAID, but the others should be set as AHCI, not Legacy or IDE.
If the last drive does not appear in BIOS when connected, you will not see it in the OS.
If it does appear in BIOS, please visit Disk Management and see if the disk appears there without Drive Letter assignment. When you connect a large number of disks, including external drives that "come and go" windows can sometimes run out consecutive drive letters which are typically assigned to disks. This can be resolved by reassigning drive letters in a meaningful manner (doesn't have to be consecutive) but you sometimes need to assign them manually if windows balks assigning them on its own. Using letters near the end of the alphabet for internal disks is usually good as this leaves lower letters for automatic assignment to removable drives which windows seems to do better with.