I installed some new .packages, and then Sims 3 failed to start.
So I delete all the cache as mentioned in the wiki, and renamed the Sims 3 folder into Sims 3 backup (mentioned in the Step 3)
The game started finally, but I have to start all over again (begin from the scratch )
How can I restore my game data where I was playing?
If everything works fine once you remove the files, put them back in one or two at a time and start the game to determine which one(s) is the problem and leave it out. If the rest don't cause problems, leave them in.
The solution is to keep following the FAQ - you stopped after the "Figure out whether or not the cause of the problem is in your user data" step, without going on to the "Figure out which file(s) in your user data are causing the problem and delete them, so your user data works again" step.
What I lack in decorum, I make up for with an absence of tact.
using the launcher (or launcher substitute) you can "uninstall" sims3packs and they will be disabled. That is usually enough. If you have something that has to actually be deleted from the ddcache, the only way to do that is to delete the entire dccache and dcbackup, then reinstall everything you -do- want.