Welcome to the Apple Discussions, Bob!
Your problem means that iTunes doesn't know where on your computer your music files are stored. And since you say it's
b all
of your iTunes songs, I'm guessing you've recently moved your Music Folder and failed to tell iTunes about it. Hopefully you know where the music is because then you can either move it back to its original location or if you want to leave it where it now is you can use the iTunes File menu > Add Folder to Library command to set things right. If you leave it where it is, you'll want to check out this post to delete the ! entries in iTunes:
MacMuse, "Removing "!" / dead links in iTunes library", 11:37pm Oct 8, 2004 CDT
One other thing, Bob, this is really an example of how your post can get lost in the crowd when you add it on to an already established thread.
Your post will be more easily noticed and you'll be more likely to get an answer by starting a new topic. To do so, click
i Using iTunes
near the top of this page and then click
i Post a New Topic
near the top of that page.
So if you have any more questions, post back but please start a new topic.