Half of my hard drives are disappearing

[wneace1]

So my computer randomly crashed the other day and took one of my sm951's with it (the boot drive)

After reinstalling windows onto a 2nd sm951 all seemed well until I realized one of my HDD's and one of my SSD's keep disappearing. Trying to figure out what is wrong.
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My system:

i7 6700k
MSI Z170A Titanium Edition XPOWER
32 gb DDR4 3000 mhz (ripjaws V)
MSI 980ti 6GD5T OC x 2
Corsair RM 1000

SM951 256 gb m.2
Corsair Force Series 480 GB SSD
Seagate Barracuda 3 TB HDD
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the below drives are disappearing:

plextor 512GB SSD PX-512M7VC
Toshiba X300 5tb
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Things I have tried:

replacing SATA cables with new ones

rebooting system (each time I reboot they reappear but they disappear at some point afterwards with no consistent time frame).

removing 1 980 ti to see if it is a power draw issue (changed nothing).

 

[RolandJS]

As a test, can you try each hard-drive by itself in the computer? For some reason, I've had hard-drives and external hard-drives "clash with each other".

 

[ArtPog]

1. After your PC "randomly crashed", did you ever learn the cause of the crash or have any suspicion why it occurred? Presumably up to that point the system functioned problem-free including the four secondary drives in the system? Or had there been prior problems?

2. And what, precisely, do you mean when you indicate "it", i.e., the crash, "took one of my sm951s" with it? Are you indicating that M.2 SSD became defective as a result of the crash?

3. Is that the reason you then installed a different SM951? You determined (or suspected) the "original" SM951 M.2 SSD had become defective? You've since verified that?

4. In any event, following the install of the new M.2 - aside from the problem with the two secondary drives - can we assume the system then booted & functioned problem-free?

5. And that's where things stand today? As long as one (or both) secondary drives are not installed, no problems with the system?

6. And there are no problems with the other two secondary drives, i.e., the Plextor SSD & the Toshiba HDD? And you've inferred there's NEVER been any problems with the system detecting those two drives, right?

7. And clarify (detail) what you mean by the drives "reappearing" upon a reboot, but then "disappear". Both drives are reflected in Device Manager & Disk Management following a boot to the Desktop, but then "disappear" from those utilities shortly afterwards? What?