I can get the game to run at Ultra high settings and it runs smooth and great, until more than one enemy of human size or larger notices me. When that happens the game slows down so much I thought it was freezing at first. It's not froze though, it's just stuttering at an extreme rate. I can move maybe a centimeter every few seconds or so and the enemies fire at me, though they and their shots stagger just as much as I do. Molerats, dogs, and radroaches don't cause this, and single enemies don't either. It's just if a group of two or more enemy NPC's of any significant size notice I'm there. Non-combatants don't cause this. I can wander around Megaton with no issues at all. It's also something that I've only run into outside, but I've not gotten far enough to tell if it happens in interiors as well.
It's not the graphics settings, it happens even if I run the game at low quality. I'm running on a Phenom 2 black edition 3.4 ghz quad core, and an AMD Radeon HD 6870 1gb video card, with 6 megs of system ram, a 750 gb hdd, and Windows 7 64 bit edition. My specs are above and beyond recommended settings. I've got several games that have higher requirements than FO3, and run them at maximum settings with no problems. This is an issue unique to FO3 it seems.
I initially modded the game, but removed them all and reinstalled with a clean install and still have the same issue. So it's not the mods either. I've tried locking the FPS, doing the multi-core fix, and assorted other fixes suggested here for FPS and still have the same issue. The game just stops cold as soon as I run into combat with more than one of anything bigger than a molerat. I've restarted the game four times now after deleting my old save files as well,and the result is the same every time. I've got gamebooster, and tried it with and without it, and I've tried tweaking all sorts of things in the .ini file to no avail. The same with updating my drivers, they're all up to date. I'm just plain stuck here.
New Vegas runs fine, so does Oblivion, and I've played through both of those games vanilla and modded quite a bit with few issues, none I wasn't able to fix anyway This is the only problem I've got with Fallout 3, everything else works great and runs smooth and beautifully. Unfortunately, it's the fun part of the game that seems to be broken here.
Any idea to fix this would be welcome. I played FO 3 on the Xbox already, but I've been looking forward to playing it again and modding a bit on the PC to freshen the experience up a little. Unfortunately, this is a game killing problem and I've pretty much run out of ideas on how I can possibly fix it. Help would be appreciated if anyone can manage it.
Edit: Got a little farther out into the wasteland messing around with it and avoiding bigger NPCs. Outside of the area just around Megaton -any- hostile NPC bigger than a mole rat brings the game to a halt, not just groups of two or more. Ran into one of the Talon Mercs and a few single Raiders, and it freezes whenever I get within say twenty game yards of them. Also, despite my HW, Fallout seems to think I should be using "Low Quality' settings. Even when I give in and let it, the problem still persists. It would appear as though I've bought two very expensive drink coasters and it's left me less than pleased. Tried a few other things, uninstalled Catalyst, reinstalled the game and gave a fresh start. Works fine until I venture out from the area around Megaton at the highest settings.
I'll probably still check around to see if a solution presents itself and poke at it a bit here and there, but for now I'm giving up. I've been at this almost three days now and there's no sign of improvement.