P67A-UD7-B3: Won't Boot (POST 26 & 4E)

[RD6]

Starting today I've been unable to access BIOS settings or Windows due to POST errors. Initial post hangs on debug code 26 (with one short beep, which usually accompanies a successful post) before resetting to what I assume is the backup bios, which then hangs at debug code 4E. System was booting into Windows this morning until I disabled PLL Overvoltage setting as well as C3/C6 States, which I thought would eliminate some of the occasional power cycling issues I was experiencing prior to this. I also manually updated the backup bios to F7 by using the ALT+F12 command at startup (This was before the other settings changes) and I was still able to boot into Windows after that. I had the Intel Turbo settings on as an overclock (x44 on cores 1+2, x42 on cores 3+4) and an XMP profile set for the RAM at 1600MHz (factory timings). Tried CMOS reset/switch button, pulling battery, alternating a single RAM module, shorting battery terminals, and checking for short circuits, but no signs of any change.

I do see the startup bios screen (with commands to get into BIOS at the bottom) when it hangs on the 4E post code but it won't accept any keyboard input.

My thought is that I botched the backup BIOS flash by not restoring to optimized defaults first and now even the backup won't post due to incorrect settings somewhere in the BIOS. But shouldn't the main BIOS post after clearing CMOS? Why is it hanging at code 26 and then reverting to backup?

Any suggestions?

System Specs:
MOBO: Gigabyte P67A-UD7-B3 Rev 1.0
CPU: Intel 2500k  (Turbo @4.4Ghz)
GPU: EVGA GTX670 FTW
PSU: Corsair AX1200i
RAM: 4x Mushkin Blackline 4Gb

[RD6]

After spending hours taking apart my water cooling loop I seem to have identified the issue: top PCI-E slot seems to have died. I was avoiding moving the GPU around as it required draining and extending my water loop, which is a nightmare as you might imagine. This mixed with the backup BIOS being flashed without optimized defaults seems to be what was making it hang and reboot during POST. I moved my GPU down to PCI-Ex16_2 slot, hooked my water loop back up, and now its making it through to BIOS settings. I then flashed the backup BIOS with optimized defaults to avoid that issue again and now I've been sitting in Windows for a few hours issue-free. Just wanted to make sure anyone who might have a similar issue with a Gigabyte board can find my solution.

Cheers!