These are the possible solutions I went through so please read every one before following it up:
NOTE: Before you start Just Cause 2, don't have the trainer running or any mods and close any open windows. Double-check your graphics drivers are up to date by visiting the Ati/Nvidia website. Disable Xfire and Antivirus for this troubleshooting. Support will not be provided to pirate copies so buy the genuine game and support the industry. I can't replicate all issues since all PCs are different.1.
Problems with heat or incorrect timings in the BIOS can cause stability issues that may only become troublesome in a particular game. If you can, set your graphics card/s fan so the temperature doesn't exceed 50*C (adjust if your particular fan is too loud). This should rule out issues with the graphics card/s getting too hot. As this game can be sensitive to overclocking, set your GPU to defaults.2.
If Just Cause 2 crashes on loading, set all graphics settings on lowest options and play for 10 minutes (most crashes happen just after 5 minutes), gradually increasing the graphics settings until you spot which option crashes your game (try playing in window mode by pressing Alt+Enter or select Window mode in Resolution options). Lower setting will help you game if its trying to use more memory than whats available to use.3.
Even a verify integrity of game cache (right-click on Steam game, Properties, then Local Files) may fix it and its always worth a try since it takes just 2 minutes. If there are no issues found, there is something else to blame.4.
If your comfortable using it, check the Event Viewer under Administrative Tools in Control Panel to see if another application in running in conflict or needs repairing. I can't provide feedback on this issue.5.
If the game crashes very often, its more than likely one of the game key components (music, textures, etc) has become corrupt - the obvious pointer to this is crashing on loading screen or even the game starting up. If your one of the unlucky ones, the savegames can become corrupt and this is why you should always have multiple saves in games.
Reinstalling has fixed most issues of Just Cause 2 crashing in all but a small proportion of users. Make sure you backup your save folder first >> Documents\Square Enix\Just Cause 2\Saves
before uninstalling. Use Run as Admin on the .exe install and install the game to another location other than Program Files if possible so the game runs with less security restrictions and hopefully fewer or no problems than before.
Finally - If none of these tips solve your particular problem, then head over to the Technical Support Forum of Eidos and provide as much information as possible.
I hope this helps fellow CH gamers enjoy their game again