Gradually moving back down to vanilla, I went to the oblivion.exe data files and unchecked Shivering Isles and it's patch- and the game finally came back to life.
I now believe that one or the other of those is corrupt and I will uninstall and then re-install the one that is.

If I'm successful, will I need to uninstall and re-install any of the unofficial patches for Oblivion afterwards?

Shivering Isles.esp is just an empty esp, all it is for is so the SI resources load. That's it.

So, the patch was corrupt then?

Maybe, might try redownloading it, and installing again, see what happens. (don't forget to rebuild your bashed patch. )

Yup, that was the problem. Game's working fine now. Thanks all.

Update 2:

Now I'm on to installing Oscuro's Oblivion Overhaul (I have all the DLCs, Tamriel Travelers, and CObl so far), and the read me says:

"Now you have a choice. You can either:
Click Add Archive and select the OOO 1.33 Complete archive -- or whichever of the OOO archives you downloaded (i.e., either OOO_132f_UPGRADE.7z or OOO_132f_Complete.7z)
Or, you can click Add Folder and select the custom 1.32.FinalComplete+1.33Patch folder you made in Step #2."

So, if I downloaded 1.33 Complete, I should use the first option right? The problem with the one is when I click Add Archive, it won't let me add a folder and there are no visible files. So, I'm not sure what to do here. I mean, when I click Add Folder, I can import the entire folder, but this says not to do that, right?

Apologies if this seems extremely meticulous, but I've learned that the smallest mistake can set me back more than a week. So, I'm being extremely careful. :confused:

I handled this problem by telling the package installer to install OOO 1.33 into a folder in Documents. I then installed the 1.34 Update into the OOO folder in Documents and let it overwrite the older esm and esp file, I deleted the Harvest Flora mod completely, and renamed the OOO folder to 00 Core files, and made it a BAIN archive using 7-zip.
Just remember to check the esps you want when you install it.
EDIT added "in Documents" I do understand the frustration, I forgot to update my initial BAIN install with esp files I have downloaded or modified when I converted from using OBMM to using BAIN.

In other words, you used BAIN (instead of OBMM) to install it? I can do that by simply copying and dragging the folder from C:\Oblivion to BAIN, right?

If it is that simple, I do not know how to do it. I created a folder inside of Documents called BAIN CONVERSION, and I just install the resources a mod needs into the BAIN CONVERSION folder. I knew that the autoinstaller created a folder named OOO, so I installed the !.34 update into Documents\BAIN CONVERSION\OOO. I keep an empty C:Program Files\Bethesda Softworks\Oblivion\Data for situations where a program with a packaged installer will not let me choose where I want the mod installed to. then I can convert the items inside the Data folder to a zipped file to place inside Oblivion Mods. I do not what you personally are using, because I downloaded OOO and the !.34 update from PES, If you use TESNexus as a source for your mods that site keeps older versions longer so a user can upgrade from OOO 1.0 to 1.34, without doing a reinstall.

It turns out that's a viable method. The game seems to work just fine. :yes:

I am glad you got OOO to work! I enjoy the changes it makes to the game, until my character dies. My favorite weapon is from OOO.