I could really use some help here. I installed Oblivion GOTY via steam. Downloaded several cool, fantastic & useful mods, turned them all into .omods, even the texture replacements that don't have .esps.
Now, when activating them one by one or couple by couple and starting up Oblivion to test wether they still work together, everything's fine, always starting up. I can install them all, loading up my character in that prison cell, save, add another mod etc. ...
Next day or next time I start my PC, Oblivion doesn't start anymore. Launcher comes up, I click Play --> CTD
I deactivate all mods via obmm - as taking away the most recent ones doesn't make a difference - just use the basic GOTY-files again. And, maybe not quite miraculously, everythings fine again.
Then I start over again, adding some mods, it seems to work fine - till it happens again for no obvious reason at all.
I use Windows 7-64bit and my settings are not recognized when Oblivion starts to automatically try to detect them.
Here's my mod-list and load order (the one proposed by BOSS):

Oblivion.esm
Open Cities Resources.esm
TNR ALL RACES FINAL.esp
TNR - ShiveringIsles.esp
Unofficial Oblivion Patch.esp
UOP Vampire Aging & Face Fix.esp
Oblivion Citadel Door Fix.esp
DLCShiveringIsles.esp
Unofficial Shivering Isles Patch.esp
Arthur_Natural_Weather_HDR_by_Max_Tael.esp
Natural_Habitat_by_Max_Tael.esp
Enhanced Water v2.0 HD.esp
Better Bell Sounds.esp
Symphony of Violence.esp
Atmospheric Oblivion.esp
Cities Alive At Night.esp
IWR-Lights.esp
IWR-Windows.esp
IWR-Shutters.esp
WindowLightingSystem.esp
AliveWaters.esp
AliveWaters - Koi Addon.esp
AliveWaters - Slaughterfish Addon.esp
ClocksOfCyrodiil.esp
CM_Better Wine_SI.esp
Cyrodilic Brandy.esp
ImprovedSigns.esp
Living Economy.esp
Living Economy - Items.esp
Improved Hotkeys.esp
DLCHorseArmor.esp
DLCHorseArmor - Unofficial Patch.esp
DLCOrrery.esp
DLCOrrery - Unofficial Patch.esp
DLCVileLair.esp
DLCVileLair - Unofficial Patch.esp
DLCMehrunesRazor.esp
DLCMehrunesRazor - Unofficial Patch.esp
DLCSpellTomes.esp
DLCSpellTomes - Unofficial Patch.esp
Adonnays Classical Weaponry.esp
Adonnays Elven Weaponry.esp
Slof's Horses HA Essential.esp
DLCThievesDen.esp
DLCThievesDen - Unofficial Patch.esp
DLCThievesDen - Unofficial Patch - SSSB.esp
Klarre Forestheart.esp
DLCBattlehornCastle.esp
DLCBattlehornCastle - Unofficial Patch.esp
DLCFrostcrag.esp
DLCFrostcrag - Unofficial Patch.esp
Knights.esp
Knights - Unofficial Patch.esp
xuldarkforest.esp
xulStendarrValley.esp
xulTheHeath.esp
XulEntiusGorge.esp
xulFallenleafEverglade.esp
xulColovianHighlands_EV.esp
xulChorrolHinterland.esp
xulBeachesOfCyrodiilLostCoast.esp
xulBravilBarrowfields.esp
xulLushWoodlands.esp
xulAncientYews.esp
xulAncientRedwoods.esp
xulCloudtopMountains.esp
xulArriusCreek.esp
xulPatch_AY_AC.esp
xulRollingHills_EV_withoutWheat.esp
xulPantherRiver.esp
xulRiverEthe.esp
xulBrenaRiverRavine.esp
xulImperialIsle.esp
xulBlackwoodForest.esp
xulCheydinhalFalls.esp
xulAspenWood.esp
xulSkingradOutskirts.esp
xulSnowdale.esp
Open Cities New Sheoth.esp
Open Cities Outer Districts.esp
Open Cities Full.esp
Natural_Vegetation_by_Max_Tael.esp
Leviathan Soulgems.esp
P1DKeyChainSI Merged.esp
PersuasionOverhaul.esp
RealisticForceMedium.esp
RealisticMagicForceLow.esp
SupremeMagicka.esp
SM_ShiveringIsles.esp
SM_DLCSpellTome.esp
SM_EnchantStaff.esp
SM_UnlockSpells.esp
SM_Scrolls.esp
SM_SigilStone.esp
Deadlier Traps.esp
RenGuardOverhaul.esp
Deadly Reflex 5 - Timed block and 150% damage.esp
DeadlyReflex 5 - Combat Moves.esp
SM_DeadlyReflex.esp
[GFX]_Initial_Glow-all.esp
[GFX]_Initial_Glow-creatures.esp
Open Cities Classic Road Record.esp

Any help would be so desperately well appreciated. Thank you.

Arthur_Natural_Weather_HDR_by_Max_Tael.esp <-- Install the fixed version, link here -> http://tesivpositive.animolious.com/?page=popular_outdated_mods

Do you have OBSE installed?

OBSE - http://tesivpositive.animolious.com/?page=obse

Installing & Uninstalling - http://tesivpositive.animolious.com/?page=installing_oblivion <-- move Steam outside of the default folder to a custom folder (i.e., C:\Games)

Thanks for the help, will try it out. As for OBSE and Steam: yep, got the former, installed the latter differently.

Please don't cross post. Use http://www.gamesas.com/index.php?/topic/1107994-oblivion-suddenly-not-starting-up-anymore/page__p__16230704__fromsearch__1&#entry16230704 and if at some point it needs to be moved to this section use the report button and ask for it to be moved rather than having two topics about the same thing.

Thanks.