There's another way to rebuild your sound library. But this would require another hard drive or a portable storage. Copy your ST3 content folder to another driver. You probably don't have to copy everything if driver space is limited. Have ST3 point to the new location and it will rebuild the library. Then point it back to the original location.
In the top right corner of ST3 there are 4 icons. Click the 3rd from right icon to access settings. Under Disk path click browse in order to point ST3 to your content folder.