PC Fallout 3 Problems.

I just got the Fallout 3: Game of the Year edition (which i got from Steam) and I loaded it and played for around 40 minuets, I was just about to get out of the vault, and i encountered a problem. My game froze, and it froze to the point where I control-alt-deleted then went to task manager and had to end my Fallout 3 task, which was not responding. So I'm running Windows 7 with a 64bit version. If anybody can help me here it would be much appreciated.