PSU Died, New PSU, Bios Won't Recognize SATA Devices, Now Won't Turn On

Synopsis: PSU died, replaced PSU with different model, system boots to bios successfully but does not recognize any devices in SATA ports, nor do those devices appear to be getting power. Now can't even get to BIOS, entire PC flicks on and off repeatedly as soon as I turn the PSU on regardless of whether I hit the power button on the front of the computer.

System Specifications

Original PSU that died: SeaSonic M12II 750 SS-750AM 750w PSU
CPU: Intel Core i5-3570K Ivy Bridge 3.4GHz
GPUs: ASUS 670 non-top version, SLI (2x)
MOBO: ASRock Z77 extreme 6
RAM: Mushkin Enhanced Blackline 8GB (2 x 4GB) SDRAM DDR3 2133
Optical drive: Sony AD-7280S-0B 24x SATA Internal DVD+/-RW Drive
SSD: SanDisk Extreme 240GB SATA 6.0 Gb-s 2.5-Inch (OS is installed here)
Storage drive: Western Digital Caviar Black 1 TB SATA III (This was not connected when power supply died)

Detailed explanation:About a week ago my PSU (Seasonic 750w) died randomly while the computer was left running in sleep . I RMA'd the dead seasonic. In the mean time I happened to come accross an extremely good deal on a new PSU, so I bought it (Thermaltake smart m850w PSU) to have a backup and to get my machine working again. I hooked up the new PSU to GPUs, CPU, fans, ATX power connector, and to all of the SATA devices, (the SSD, the HDD, and the Optical drive). I made sure to connect the data cables to the SATA devices in the same configuration they were in when working properly. The computer boots successfully to the ASROCK BIOS, all fans spinning. However, I get the error code "A6" on "dr debug" (the led display on the mobo). The manual says this means "SCSI detect". I have no idea what that means.

I was able to load the UEFI, and bios recognized all components except for any of the SATA devices--(SSD, the HDD, and optical drive not recognized). The RAM, GPUs, processor, and fans were detected. At this point I was stuck in BIOS because I couldn't boot off anything.I did not have the HDD connected when the PSU failed, but now the BIOS won't read that either. I don't think any of the SATA devices are actually receiving power. Again, the UEFI showed that there were no SATA devices connected to any port, when in reality they clearly were connected both by power and data cable. Then things get really strange. I unhooked all of the SATA devices except the HDD (the one that wasn't hooked up when the original PSU died). I plug the AC into the PSU, then turn on PSU (not the power switch for the computer, the switch on the PSU). The computer starts flicking on and off in this weird rhythmic pulsating pattern "click...click...click...click..." with about a 1/2 second between each click. Each time the power flicks on, the LEDs come on and the fans spin briefly. The strangest part is that I don't need to hit the power button on the front of the case for this to happen, it just starts as soon as the PSU is turned on. In fact, I can't get the computer to turn on at all--the switch on the front of the computer appears to be dead.

1. Unplug the power cables from everything and re-seated them.

2. Reseated the data cables to the optical drive and the SSD on the drive end, not on the MOBO side as they are covered by my GPUs and I would have to take them out in order to do that.

3. Tried hooking up a SATA power cable from my old modular PSU and using that in the new PSU in an attempt to power the optical drive (didn't work, I know, bad idea--I learned you aren't supposed to do this shortly after I tried it)

4. Setting all preferences to default in the UEFI.

5. Disconnecting the power cables from one or both of the GPUs.

I think that this is either a problem with (1) the motherboard, (2) the new PSU, (3) all 3 SATA devices (unlikely). The fact that I can't even get into Bios anymore tells me that this may be a MOBO or PSU issue.My main question is how to procede from here? I suppose I can wait for my Seasonic to come back from RMA--perhaps that will clear up the issue. I just can't shake the feeling that this is a MOBO issue though. I am worried that if I keep screwing around with it I may end up frying my CPU and GPUs. I can eat the cost of a MOBO or PSU if necessary, but I can't afford to buy a new processor and two new 670s.