Ok, so if I understand right. You stopped playing FO3 5 months ago and never uninstalled and have now come back to play again?
OK. Have you been using your PC for other things, like other games, browsing the net and installing PC and hardware updates? All this could`ve changed your computer settings\configs in such a way that FO3 now has a bit of a problem working right. Maybe you now need to check your graphic drivers, or update fO3 somehow, etc. I wouldn`t immediately blame Mods.