So as the title says, I can't do shift-click on mailbox anymore which is weird because I can do it on the ground and on sims. Lately I installed the Quicker Painting and Body Shape Slider. There's a possibility one of them cause this. I can't delete the mailbox with sledgehammer tool nor can I delete it with "Shift-Click, Object, Delete". I even tried move my sims from that house and the new house's mailbox also broke. I've deleted all mods from my Mods -> Packages folder and still not working.

And I'm pretty sure it's the Quicker Painting makes my Sims 3 can't exit the game and go to main menu properly, I have to use Windows Task Manager to end process. But for now, please help me with the Shift-Click Mailbox problem. Pleeeaasee.

Moved to help!

Ok. You said you removed all mods from Mods/Packages, and it didn't help. I'm assuming that you also remembered to clear the caches when you removed the mods? (Caches hold information so that it doesn't have to keep being reloaded. But the cache often still holds information from mods that have been removed, or it can prevent data from being loaded by a new mod because it thinks that everything relevant has been loaded. Or data in the cache can get corrupted. If you delete the cache, the game generally rebuilds it.)

If you've still got the problem after removing your mods and clearing the caches, it's time for the next step.

Rename your entire Documents/Sims 3 folder. Then run the game. It will create a new folder and a new, vanilla, game. if the problem is gone, you can start moving the contents of the old folder to the new one. Do one subfolder at a time, and test after each one. When the problem comes back, it's in the folder you just moved in. Then you can take that folder out and do a binary search through it to figure out what was causing the problem. (remembering to clear caches after each step) If you're pretty sure it's a mod that is causing a problem, I would leave that mod for last. And if the problem is still gone after everything is back into the game, I would just enjoy playing. Sometimes the game just gets temporarily confused by something.

Hi, Ghost sdoj, thanks for your answer. I did delete the cache files and the problems still there and I have not try to make the game back to vanilla yet. But I discovered something, I tried to make a new game in a different town and there's no problem in it. The Shift-Click on mailbox is working fine, even the exit program or go to main menu problem is gone. And then I put all my mods back in the Package folder, play a new game, save game, quit game, load game, and still fine. So it's my save game that's broken. There's no way to fix it, is there?

Try going back to the save game in question. It might be mysteriously fixed now too.

I think I found a way to rescue my save game. I copied my house to library and start a new game then I move in my household from library to my saved lot. And the problem is gone! Phew!

I'm glad you got it solved!