This is driving me crazy and I hope someone can help steer me in the right direction. I hope I've posted this in the most appropriate forum, so here goes:
First, refer to my basic system specs as a start.
My problem is that my motherboard BIOS intermittently recognizes my four hard drives during bootup. On reboots, it will sometimes recognize drives 1,2 &,3, or then drives 1,2 &4, or maybe 2,3 & 4 (resulting in a "no boot", obviously), or maybe just 1 & 2.
It's all over the place and it's driving me nuts.
To date, things I have tried have been to:
1. Changed out the SATA cables themselves.
2. Bypassed the SATA panel altogether and attached the drives directly to the MB.
3. Changed out the MB itself with an RMA from Asus.
4. Reinstalled the newest SATA drivers from Asus specified for my MB.
5. Made sure that I'm running the latest updates for my Win7/64 operating system.
6. Am using the newest BIOS from ASUS for this MB.
Here's where I'm at:
At times,
all of my 4 hard drives have at one time or other
been recognized by the BIOS on bootup.
At times,
all of my 4 hard drives have
not always been recognized by the BIOS on bootup.
NONE of the things I've tried in items 1 through 6 above have affected the random (and frequent) occurance of the problem in any way. None of those things have made the problem any better, nor any worse.
Almost every reboot yields a lost drive of one or more of the four.
It is most definitely a problem in the BIOS and not in Windows because the post list on bootup is where it shows which of the drives weren't recognized even before Windows begins to load. Of course, what is supposed to be a lightning fast boot is agonizingly slow because Windows hangs for a while before finishing the load due to it's (Windows) trying to deal with an attached hard drive not responding.
But again, the loss of the drive is first happening at the BIOS level even before it gets passed to the Windows System loadup.
This condition continues to this day and is still an intermittent issue.
What I'm down to now is that after trying all the above, it "appears" that it could be a power issue. That is, I'm wondering if the drive array (it is not set up for RAID... just 4 drives) isn't getting enough power on boot up.
The reason I say that is not because I believe that's the problem, but because it acts that way. If a drive doesn't spin up right away on power-up, it's possible that it won't send good info to the MB BIOS as it boots and results in a no-show for the drive in the bios.
Note that drive C is an SSD drive, so this shouldn't actually be the problem because even drive C is sometimes not recognized by the BIOS (there's nothing to "spin up").
What I'm saying is that a lack of power is how this computer is acting at this point after having tried so many other remedies and not making any difference. With an AX 850 Gold powering this system, a lack of power doesn't actually make any sense as far as I can tell, and if that were indeed the problem, then perhaps the AX 850 Gold itself is defective but I don't really know how to test for that.
I'm hoping that someone can point me in the right direction here because I'm "this close" to trashing most of this system and starting over. It's becoming that frustrating after dealing with this for many weeks and still not ending up with a dependable system.
The Asus people have been most gracious so far by RMA'ing the MB itself, but the replacement behaves exactly the same way so I believe that I have eliminated the MB itself as being the problem.
Help!... 
Intermittent Recognition of Hard Drives - Long
Threaded Mode