Like many gamers, I bought a copy of Just Cause 2 during the Steam Summer Sale and if the forums are any indications, I was not alone with Just Cause 2 crashing repeatedly. Specifically it would crash on fullscreen settings.
The immediate fix was to open Steam's game library and right click on Just Cause 2 and then select Set Launch Options and enter /failsafe. This forces the game to launch in windowed mode. The game ran just fine for me in windowed mode.
However, I was not satisfied that I couldn't play this game in fullscreen so I did the normal checks to see what may be causing the issue. First I verified the game files on Steam and the check completed without error. Next, I made sure it wasn't Steam community causing the issue and with the community overlay disabled, it still crashed.
The final step I took was to upgrade my nVidia drivers. I opted to not only upgrade my drivers, but also to do a clean install of the driver in the process (which is available with the nVidia installer now). This cleared out all old profiles and other settings.
After the upgrade and a couple PC reboots, Just Cause 2 started and ran just fine in fullscreen. I hope this post helps anyone else having this issue.