The exclamation point next to a track title in iTunes means that iTunes cannot locate the file associated with that track (original file cannot be found).
You'll see that if you attempt to play one of these tracks from iTunes, you'll receive an error. This is because the music file has either been moved or deleted from the original place that it was stored. When it was added to iTunes, iTunes saved the file path that it needed to follow every time it needed to access the song. Now that the file is no longer where iTunes expects it to be, iTunes does not know where to find it.
If you think that the songs marked with exclamation points can still be located somewhere on your hard drive, you may be able to correct their media file path in iTunes as detailed below:
If the music files are no longer stored on your computer's hard drive, it may be best to remove these track listings from your iTunes library.
Tune Sweeper can help you clean up your library by removing missing tracks, deleting iTunes duplicates and fixing nameless and incorrectly labeled songs in iTunes.