Failure to start

[Xanthe_]

''fatal error;could not load world file'' what's that??any help..

Try check gamefiles with Steam defgrammer itself, whats its says? Or Verificating one.

-From the My Games tab, right-click on -game- and select Properties from the menu.
-Select the Local files tab and click the Verify integrity of game cache... button.
-Steam will verify the game cache files (GCF's) - this process may take several minutes.
-Once the process is completed, the Check Window will automatically exit.
-Restart Steam.
-Do it again.

"rename the ClientRegistry.blob and restart Steam."

Change Downloading Region:

On Windows

Start Steam
Go to Steam > Settings > Downloads tab
Under Download region, select a different but relatively close region.
Try launching or installing the game once more

On Windows

If the issue is isolated to a few Steam games, please exit from Steam and go to the Steamapps folder (default is C:\Program Files\Steam\Steamapps) and delete any listed .ncf files for the specific games. Once complete, please restart Steam to test the issue.

Source Google and this. Defrag your hard drive aswell.