Question Calling all experts - ASRock X99M Extreme4 slow death

[DernBoy]

I've got an older rig I've demoted to a headless RDC system that I sometimes fire up for some animation rendering. But it has been acting weird lately and is now dead in the water. Maybe some folks here can give me a few extra noggins to bang on.

ASRock X99M Extreme4 motherboard with two P1.80 BIOS chips (A-B switch)
Intel i7-5820K CPU
G.Skill Ripjaws 4 Series (4x8GB) DDR4 SDRAM
EVGA GTX 960
Muskin Enhanced Reactor 256GB SATA III SSD
700W ATX PSU
Windows 10 Pro x64

History of wackiness:

Since demoting it to a Remote Desktop PC, it used to bark at me for not detecting a mouse or keyboard. Since I don't have a display connected to it, I just got used to it and gave it a little extra time to boot before connecting to it via RDC. This worked for a few months until it started not coming to life AT ALL. No beeping, no whirring, no lights. I tried a different power cable so I could get a better look at it without it being up on a shelf. Just having a different power cord actually worked for a few sessions... until it didn't. Then I ordered a new PSU.

The new PSU behaved the same way! No lights or nothing. So, I started unplugging things and hooked it up to a display and keyboard. I also reset the CMOS.

After a few bouts with false hope, I'm currently in this situation:

No errors upon booting, but my SSD drive is not recognized by the BIOS. I plugged the same drive into one of those USB external boxes and plugged it into another PC and it popped right up. I've tried a few of the many SATA3 ports on the board and swapped out a few of the power leads to the drive and no dice.

I ordered a single BIOS replacement chip from some vendor on eBay, but I don't know if that was a waste of money or not. I'm also considering a new CMOS battery, but I figured 4.5 years old shouldn't be an issue.

Any Obi-Wans out there that want to lend this doofus a hand? Let me know if any info is missing or unclear.

Much obliged!

 

[popatim]

When you replaced the PSU, did you reuse the old cables?

 

[DernBoy]

The old PSU didn't have modular cables, so, no. I also used a different data cable.

I also flashed the BIOS to 3.50 since my first post. No difference.

Thanks for the suggestion.

Update:
After using the power lead from a second HDD that I had simply unplugged the data cable to, I was able to get the BIOS to recognize the SDD boot drive reliably. However, Windows was giving an error on boot INACCESSIBLE BOOT DEVICE and kept trying to diagnose and repair in an endless loop. After messing around with some AHCI settings, etc., I finally got it to boot in Safe Mode.

I feel about 50%-50% on whether or not this is fixed though. I'll let it simmer a night and see what comes next. I don't need to run this machine with a second HDD or optical drive anymore anyway.

I just wish I knew why this thing went so wobbly on me.