Ok so I've had Fallout 3 for about two years now, and its worked fine (at least mostly). I've had occasional crashes and a few bugs but nothing I can't just get around but starting about yesterday it barely runs anymore. It runs fine for about 30-60 seconds and then hangs, audio is still working fine but video is frozen. 90% of the time it results in a crash to desktop (where the screen goes black and then it CTD). I haven't installed anything new or done anything to the game so I have no idea why this is suddenly happening. This problem started happening the other day, like I said, but it was once every 10 mins or so and kept happening more often until now its down to 30-60 seconds of game time. Its takes me longer start the game, log in and load then it does to play it before it crashes.

Specs:
Windows XP SP3
ASUS P4P800 SE Motherboard
2.66 Core Duo Processor
EVGA GTX 260 (Patch 182.50 - Can't go any higher without running into problems but its the same version I've had for the past year or so)
4GB Ram

EDIT: I should also mention that I have an original copy of Fallout 3 (not GOTY) and its not linked through steam.