There was an error during startup, please see the log for more details?!?!

Try temporarily moving your Sims 3 folder from My Documents \ Electronic Arts and put it on your desktop.

Then try to launch a game. You won't have any of your installed content or games in this new game as those files are in you Sims 3 folder on your desktop now. But that folder often gets corrupted and can cause problems.

If you find you are now able to successfully launch a game, then you will need to work out how much you can move from the folder on your desktop to your new Sims 3 folder. You will also need to reinstall your store content.