Imported furniture and textures are not stored in Sweet Home 3D installation folder, but in a user folder which location depends on your system. For example, under Windows Vista to 10, they are stored in C:\Users\user\AppData\Roaming\eTeks\Sweet Home 3D where user is your login.
Thus, if you want to get back your catalog data, you should rather copy the files found in this folder as explained in this thread. If you didn't save these files, I fear you'll have to import again all your 3D models. [:(]
One last thing: the imported furniture and textures used in .sh3d files are copied in these files, so don't worry for your designs, they won't be broken.