I'll chip in just to concur: start again from the top.
Modding Oblivion can be very satisfying, especially if the modding bug bites you and you start writing your own mods to tweak your game to be exactly what you want. But it can also be exceedingly frustrating if you don't do it properly and make use of all the excellent
tools available.
- Uninstall and reinstall vanilla oblivion. BACKUP THAT FOLDER for reference and just-in-caseiness.
- (Re)Install any utilities you need: http://obse.silverlock.org/, Construction Set (Extended), http://www.nexusmods.com/oblivion/mods/22368, https://github.com/boss-developers/boss/releases/tag/v2.3.0, http://www.nexusmods.com/oblivion/mods/39215, http://www.nexusmods.com/oblivion/mods/11536/?, http://www.nexusmods.com/oblivion/mods/43277, http://www.nexusmods.com/oblivion/mods/15781 at the very least. Make certain these are all running properly.
- Install a mod or two. Start with simple things, UI improvements or things like alternative start or a drop lit torches mod or.... Don't start with a full suite of city and landscape overhauls all in one go.
- Rebuild your bashed patch. Rebuild your LOD if needed.
- Fire it up and make sure things work. Run around for 30 minutes, fast travel, kill stuff, talk to people, go in and out of cities and dungeons, pick locks... especially test things that are affected by the mod(s) you just installed.
- Rinse and repeat.
I also can't stress enough the utility of Wrye Bash: make well-organized BAIN archives of everything you install (don't assume that an archive is BAIN-ready when you download it, it's likely not) and your installation and especially uninstallation of mods will be so much easier and more reliable.