If your Spotlight index becomes corrupted, Spotlight will stop returning search results. No matter how wide open you make your search, it'll tel you that there are no matches. If Spotlight keeps giving you no matches, here are the steps to take to rebuild the index and fix things.

1 - Open a terminal window.

2 - In the window, enter this command: sudo mdutil -E /

3 - Confirm the admin password for your machine.

4 - Wait.

Once you enter the command, Spotlight will rebuild the search index it uses from scratch. This can take several hours. But when it is done, Spotlight will be working again.