I accidentally unplugged ny boot drive, thinking another of my 6 hard drives was the boot drive - realized what I'd done and plugged it back in, but nopw it doesn't appear in the boot drive options, so I was forced to go to boot override choices to select it. Now I have to do that after every shutdown.
Trying to cure that, changing settings, it then wouldn't boot from override. Used F8 which led me back into bios showing me a full list of drives ...
That got me in, but on restart, even though the C drive is now selected in boot options, I still have to go to boot override to successfully boot....
If the Rampage V has the BIOS user profiles feature which allows you to save the current config, you could try saving your config then using "load optimised defaults" to see if that changes anything. If your boot drive is on the first SATA port, I'd expect it to be selected by default (assuming it's still a valid boot device, which sounds like it is the case if override works). If that doesn't help the diagnosis process, you can just load your old config from the user profiles and you won't have lost anything.
If that does get it working, you can then work on figuring out what setting is making the difference.
The drive numbers reported by Windows are just based on the order it scans drives (usually determined by the way the hardware is built). Assuming a normal-ish install with boot/system/Windows on a single C: drive, no RAID or similar, and assuming you are not using SATA Express, connecting that drive to SATA6G_1 should keep things simple and make it appear as the first of the SATA drives and cause the BIOS defaults to automatically select it as the boot drive.
If that involves swapping drive connections around, take good notes on what's connected to each port before you change anything, and on what it looks like in Windows Disk Management. The key thing is to see if you can get the boot problem solved. If that solves booting, you've ruled out the drive as a source of the problem.