Why is my Fallout 3 acting up when I start it up?

When I try to start up Fallout 3 it closes and there is a box that pops up saying "Fallout3 has encountered a problem and needs to close. We are sorry for the inconvenience." and it has ons saying "DeBug", "Send Error Report", and "Don't Send Error Report". I tried restarting it, updating Games for Live and Fallout 3, and reinstalling Fallout. What's wrong?