Changed PSU now: Reboot and select proper boot device or insert boot media in selected boot device and press a key

[SLP Firehawk]

Hi all. I have ASUS P9X79Pro. It has all Samsung SSD 2.5" drives. C: is connected directly to MB I believe. I have several other SSD drives connected via a LSI SAS card
like this: https://www.ebay.com/itm/Genuine-LS...ay&campid=5336641285&toolid=10001&mpt=6463299

Been working pretty well for a long time until I changed the Corsair AX 860 PSU today to a Corsair RM850 suspecting the PSU might be getting weak since I was having some display driver stopped working and recovered errors. The RM 850 wouldn't power on at all (even though it was working from the system I removed it from) so I put the RX 860 back in and when powering on the system it booted for a second and then went off for a few seconds then booted. But it cannot find boot drive. It only seems to detect one of the optical drives and the multi card reader.
1st photo shows all the drives when they were working properly.
2nd photo shows the boot screen which should have several drives listed but doens't now.
3rd and 4th pic are bios screens which only show the media card reader and optical drive for boot selection.

Please help. I really need this machine to work again. Win 7 Pro SP1.

 

[SLP Firehawk]

I unplugged all the SATA drives except C: same error.
I removed the LSI SAS card. Same error.
It will not detect C: drive or the other drives no matter what I try.
And strange thing is whenever I shut the power down on the PSU and unplug it, it always has a strange boot afterwards - it boots for one second then shuts down for a few seconds like it loses power and then starts up again and POST

 

[SLP Firehawk]

Removed the PSU cover this morning and found a SATA power connection loose somehow going in the 6 pin on the PSU. Plugged that in and it booted to a new Megatrends screen showing all drives but saying C: was bad. Went through several more boots, plugging unplugging cables and with the "disk read error occurred" and also "..reboot and select proper boot device" messages. The 2TB C: did eventually show up on the BIOS screen and when I selected it the machine did boot to windows (the 2nd time around).
attached are pics of the order. Obviously the unplugged cable wasn't getting power to most of the SSD drives but the other problems I do not understand.
Is my PSU failing? Or the new Titan GPU I just replaced the failed Titan GPU? Or the Motherboard? Or GPU driver?

 

[spine]

I've had sata cables die over time, so double check yours are all good. Faulty sata cables can cause weird things that don't seem like sata drives failing. I myself have replaced a PSU in the past only to find it was infact, one dodgy sata cable.

As for the weird power off/power on first time after removing PSU, that's normal for modern motherboards these days. Often they can power cycle or 2 times before finally actually booting/posting.