Question M.2 SSD install causes VGA debug light, but shouldn't ?

[tduggan2]

overview: Had blue screen issues with Windows, which had been running fine off a SATA SSD. It's a 5+ years old SSD. Figured it might be failing as I was having difficulties running "RESET MY PC" in Windows 10 Recovery environment. Got a new M.2. NVMe SSD to replace it but now POST gets hung up on "VGA" (LED staying on red on the EZ Debug indicator on the mobo.)

system:

• MSI x470 Gaming Pro Carbon
• AMD Ryzen 7 2700X - YD270XBGAFBOX4x Corsair Vengeance LPX 16GB DDR4 DRAM 3000MHz C15 (CMK16GX4M2B3000C15)
• GeForce GTX 1070 Amor 8G OC
• Thermaltake 600W PSU
• WD_BLACK 1TB SN770 NVMe Internal Gaming SSD Solid State Drive - Gen4 PCIe, M.2 2280 - WDS100T3X0E

behavior:

• with only CPU, RAM (any config), and GPU in PCIE_1 slot (3.0 x16):
  MOBO POST gets hung up on boot ("boot" light on EZ Debug indicator stays on. "VGA" and "CPU" lights turn on and then off. everything seems to work as normal).

edit - with the above conditions, I CAN access the BIOS. I am currently attempting a BIOS update fingers crossed*

• with only CPU, RAM (any config), GPU in PCIE_1 slot, and SSD installed to M.2_1 slot (PCIe 3.0 x4):
  MOBO will not POST, but it gets hung up on GPU ("VGA" light stays on red)

alternatives:
I've tried all permutations of installing:

• the NVMe SSD in M.2_1 slot and M.2_2 slot (PCIe 2.0 x4)
• the GPU in PCIe_1 slot and PCIe_4 (3.0 x8) slot

same things happen

theories:

1. I looked into the idea that using the M.2 slots may make the PCIe slots unavailable but the manual seems to think my configs are alright It says this:

-SATA1 port will be unavailable when installing SATA M.2 SSD in M2_2 slot.
-PCI_E6 slot will be unavailable when installing PCIe M.2 SSD in M2_2 slot.
-M2_1 slot only supports PCIe mode.

1. no indications of defect or damage I can figure unless this brand new SSD is defective. I haven't yet gotten to test it elsewhere, but I have an external enclosure I can put it in. I'll try that. I also have an M.2 to PCI-e 2.0 x1 adapter thingy on-hand that maybe I'll use to plug it into the mobo just to see if it shows up. I also have some other old NVMe laying around. Might try that as well.

Thoughts? What am I missing here?