Sometimes, just stopping and re-starting Spotlight will do the trick.
This is pretty easy just launch the Terminal and type the following:
sudo mdutil -a -i off
This tells Spotlight to disable indexing on all volumes – your Mac will prompt you for your administrative password.
Re-enabling Spotlight is just as easy, just reverse the off to on:
sudo mdutil -a -i on
Now Spotlight will be back on and hopefully will index as usual.
