Move your Sims 2 Legacy folder onto your desktop. Start the game and see if it starts up properly. It may be slow because it has to generate new files, but if it does, then something was corrupted in one of your folders.
Go into the new Legacy folder the game generated, drag out one of the neighborhoods, then drag in that neighborhood from the file on your desktop. Start up the game and see what happens. If it starts up fine, then do the same with each neighborhood and check to see what happens after each. If it crashes again after adding any one of them back, then it was something in that file and you will need to keep the new one. If the game continues to load up fine after you've restored all of your neighborhoods, then it was some other file.