Hello everyone... I bet this part of the forum is bursting with "Oblivion won't start issues" but I really hope someone could assist me.

A while ago I reinstalled Oblivion with a considerable amount of mods (+patches and updates too ofc). I've never had so many complicated mods so I settled for not being able to play my old saves, because I wasn't even sure if the game itself would start! I installed OBSE, for example.
Now after another while I thought of playing Oblivion again, I didn't remember to launch Oblivion with obse_loader.exe and used the regular Oblivion launch menu instead, and now it won't work! It crashes immediately. I tried overriding the obse_loader.exe and I tried launching Oblivion via OBMM but neither option worked. Is there anything to be done? I seriously wouldn't want to go through the process of installing all the extra stuff again (it took me hours)! I am no genius with mods : (

Thanks in advance.

I've had a history of epic failing with OBSE but i'm fairly sure you have to start Oblivion with the OBSE launcher.

Disable all your mods and try to load with only the Oblivion master file.
From what your discribing I feel the issue isn't OBSE related.

No, it will not start :/ Only the Oblivion.esm was abled and it still insta-crashed via launcher, OBMM and obse_loader.exe. Like I said, it previously worked with all the mods but when I accidently tried starting it from the game launcher (when I should have used obse_loader.exe) it started crashing.

Try the simple fix first.
Find the game ini in My Documents\My Games\Oblivion and rename it (anything will do). Restart your game with only the Oblivion esm and a new file will be generated.
If this works it's then safe to delete the original. Be aware any custom alterations will have to be done again.