Mac Pro 5,1 - Cant Access Boot Menu

[JDLang76]

Fresh install of sierra and windows 10.
Have ruled out EVERY piece of hardware except logic board.
Problem is simple but Im 6 hours troubkleshooting in with no results.
When I hold down option key (using wired genuine apple keyboard-tried 2) I get the chime but then I get nothing but a slightly increased fan noise. It stays stuck. My display detects ouput, but the computer goes no further. If I press the power button to shut it down, it shuts down instantly, letting me know its not getting any further.
I have tried everything I can think of.

Help please!

 

[casperes1996]

I mean, not to be captain obvious, but you say you've ruled out every piece of hardware aside from logic board; What GPU are you using, and does it support UGA or GOP?

 

[JDLang76]

Using stock 5770. Tried stock gt120. Also tried supported 7850. Same results. It WAS working a couple of days ago. So GPU support wont be the issue.

 

[casperes1996]

Using stock 5770. Tried stock gt120. Also tried supported 7850. Same results. It WAS working a couple of days ago. So GPU support wont be the issue.

And it works boothing into an OS, just not the pre-boot environment? Have you tried the usual; Reset SMC/NVRAM?

 

[JDLang76]

And it works boothing into an OS, just not the pre-boot environment? Have you tried the usual; Reset SMC/NVRAM?

Yes a million times. And it does boot into Sierra and Windows 10 no problem
[doublepost=1551377470][/doublepost]I just had an idea. Firmware???? Im gonna see if theres a firmware update. Maybe something got buggy for some weird reason

Whoa. Ok. Somerthing buggy going on. Booted up a sierra SSD. Used full high sierra installer. Prompted for firmware update. Did it. Help power button until flashing/tone. Then black screen for 3 minutes. Then restart into OS. Never saw firmware update bar. Re-tried high sierra install. Got the firmware messsage again. What could be going on? Have never seen anything like this before.

Update again

Put a stock GPU back in. Trtied again. Firmware update worked. HOWEVER, I did not see the grey screen and progress bar. And still no boot menu. Im thinking the issue is narrowed down to no GPU will display anything pre-OS. Why?

Update Again

Tried DVI ports on both GPUs instead of Mini DP / HDMI. On one GPU, I got a boot menu with fuzzy screen. On another GPU, I cant get boot menu but it loads into OS with fuzzy screen. HDMI / mini DP totally normal loading into OS on both cards. What the flip?

FINALE UPDATE
No one seems interested but just in case... Going with blown capacitor on logic board. Replacement is on its way. That will be all. Peace.