Active Mod Files:00  Fallout3.esm01  Anchorage.esm02  ThePitt.esm03  BrokenSteel.esm04  PointLookout.esm05  Zeta.esm06  Unofficial Fallout 3 Patch.esm  [Version 1.2.0]07  Destruction.esm08  CALIBR.ESM  [Version 1.3]09  xCALIBR.esm0A  FOOK2 - Main.ESM0B  FOOK2 - [DIK] DLC Improvement Kit.ESM0C  Mart's Mutant Mod.esm0D  Enhanced Weather - Rain and Snow.esm0E  Xepha's Dynamic Weather.esm0F  DCInteriors_ComboEdition.esm10  Unofficial Fallout 3 Patch - Operation Anchorage.esp  [Version 1.2.0]11  Unofficial Fallout 3 Patch - The Pitt.esp  [Version 1.2.0]12  Unofficial Fallout 3 Patch - Point Lookout.esp  [Version 1.2.0]13  Unofficial Fallout 3 Patch - Mothership Zeta.esp  [Version 1.2.0]14  Project Beauty.esp**  Project Beauty- Broken Steel.esp**  Project Beauty- Point Lookout.esp15  DarNifiedUIF3.esp16  CASM.esp17  Sprint Mod.esp18  Auto Aim Fix v1.1.esp19  GalaxyNewsRadio100[M].esp1A  Stealth Kills Enabled.esp++  Stealth Kills Enabled - Pitt Compatibility.esp1B  HouseholdWaterPurifier.esp1C  VDSC.esp1D  Persistent Skill Books.esp1E  Bottle That Water Alternative - Option A - BS.esp  [Version 1.2]1F  SniperZooming.esp  [Version 1.5.0]20  DCInteriors_DLC_Collectables.esp21  FOOK2 - Main.esp22  FOOK2 - [DIK] DLC Improvement Kit.esp23  FOOK2 - Main [Hotfix].esp24  FOOK2 - DIK [Hotfix].esp25  FOOK2 - DUI Grenade Fix for 11 Open Beta.esp26  WeaponModKits.esp27  WeaponModKits - FOOK.esp28  WeaponModKits - OperationAnchorage.esp29  WeaponModKits - ThePitt.esp2A  WeaponModKits - BrokenSteel.esp2B  WeaponModKits - PointLookout.esp2C  WeaponModKits - Zeta.esp2D  ReneerInvisibleKarmaMod.esp2E  Wasteland Whisperer.esp2F  RobCo Certified.esp30  Mart's Mutant Mod.esp31  Mart's Mutant Mod - DLC Anchorage.esp32  Mart's Mutant Mod - DLC The Pitt.esp33  Mart's Mutant Mod - DLC Broken Steel.esp++  Mart's Mutant Mod - DLC Point Lookout.esp34  Mart's Mutant Mod - DLC Zeta.esp++  Mart's Mutant Mod - Hunting & Looting.esp35  Mart's Mutant Mod - Natural Selection.esp++  Mart's Mutant Mod - Reduced Wasteland Spawns.esp++  Mart's Mutant Mod - Tougher Traders.esp36  Mart's Mutant Mod - Zones Respawn.esp37  Mart's Mutant Mod - FOOK2.esp++  Mart's Mutant Mod - FOOK2 - DIK.esp38  BLTC.esp39  BLTC Immersion Patch.esp3A  BLTC Hypo Fix.esp3B  BLTC Less Addictions.esp3C  Arwen_SmarterAI.esp++  Arwen_MMM_Patch.esp3D  Realistic Interior Lighting.esp**  Realistic Interior Lighting - BS.esp**  Realistic Interior Lighting - OA.esp3E  Xepha's Dynamic Weather - Main.esp3F  Xepha's Dynamic Weather - Anchorage.esp40  Xepha's Dynamic Weather - The Pitt.esp41  Xepha's Dynamic Weather - Broken Steel.esp42  Xepha's Dynamic Weather - Point Lookout.esp43  Xepha's Dynamic Weather - Rain (OA).esp44  Bashed Patch, 0.esp

So yeah, my game is now unstable and I don't know why. It crashes after only a few minutes in the game at completely random intervals. There doesn't seem to be any sort of obvious cause either.

I'm going to venture a guess...

Unofficial patch mod. If you don't "need" it, don't use it. I was using it w/o needing it and suffered many crashes after installing it at random intervals as well. I would suggest possibly un-checking it in FOMM and seeing how your game performs.

I had the exact same issue about a month ago (http://www.gamesas.com/index.php?/topic/1083266-ctd-about-every-five-minutes/page__p__15782687&#entry15782687).

I installed the http://www.fallout3nexus.com/downloads/file.php?id=6510, and it fixed my crashes.

I can't promise you that this will solve your CTDs, but it's a small download, and if you KEEP A BACKUP of your original Fallout3.exe file, it is easily reversed / uninstalled. So it's worth a try.