Steam: Fallout 3 failed to start (error code 80)
Here’s a really quick one: I kept getting this error when I tried to launch my recently purchased copy of Fallout 3. I googled around a bit, and while I found people with the same problem, no fixes were available.

Fallout 3 failed to start (error code 80).
Solution
While not an actual solution, I’ve been able to circumvent this problem by closing Steam, and re-opening it. This will allow you to launch the game successfully, but only once. If you quit the game, and try to launch it again, it won’t work. To get it to launch again, simply repeat the process – close Steam, re-open it.
I’ll try and figure out how to fix this once and for all.

I am having the exact same issue with Bad Company 2…except that it does not work whether or not i re-start steam ;(
Try:
- Activating the beta or normal UI, whichever you're not using. (Steam > Settings > Beta Participation)
- Creating a shortcut to the game executable on your desktop. Find the executable within the Steam directory. Make sure sure to enable the "Run this program as an administrator" field in the Properties > Compatibility section of the desktop shortcut. (applicable to vista/7 only).
I'll take another look at this tonight.