Re: Installed Prism Art Studio, but the 12 items that come in the pack can not be found.

Try this from the Store FAQ

I installed my Store Content but it's not showing up in my game

Unfortunatly, the Launcher is a very unreliable tool. The more stuff you have, the greater the chance that files which have your stuff installed get messed up. If that starts happening to you. It's best ro reinstall all Store content, using this method:

• Close your game and launcher
• Go to documents\electronicarts\thesims3 and move the folder DCCache to your desktop (this is ALL your custom content, so if you have 3rd party content as well, you might wanna just move the *.ebc files as well as the missingdeps.idx)
• If you have any worlds installed go to the installedWorlds folder and delete all Store worlds from there.
• Go to the DCBackup folder and delete everything in there. You don't really need the stuff in here except for the ccmerged file but since you're reinstalling everything, it will be recreated.
• Open the launcher and start reinstalling all store stuff in groups. Don't install all in one go. Start with the worlds, then lots, then sets and single items last.

When you're done, backup the DCCache folder. If the same starts happening again, go back to that backup so you don't need to start over. Make a backup from time to time, especially after you've installed worlds and lots.