Hello M-P-H83,
Thank you for using Apple Support Communities.
I understand from your post that you have moved your iTunes Library to an external hard drive and now the iTunes Library in iTunes has exclamation marks next to each song. Keeping your music on an external hard drive is a great way to save space on your Mac.
I recommend changing the location information within iTunes so it points to your external hard drive. This article has the steps you can use to change the pathway to your files on your external hard drive:
Locate and organize your iTunes media files
On the Advanced tab:
- Look in the box under "iTunes Media folder location" for the location of your iTunes Media folder.
- To change the location, click the Change button and enter a new location.

After you change the location of the folder, existing files won't be moved unless you consolidate your files. To consolidate your files:
- Mac: From the menu bar at the top of your computer screen, choose File > Library > Organize Library and select "Consolidate files." Then click OK.
- Windows: Hold down the Control and B keys to open the iTunes menu bar. Choose File > Library > Organize Library, and select "Consolidate files." Then click OK. Learn more about menus in iTunes for Windows.
Best Regards