I believe the solution is fairly simple.
First, quit iTunes (if it is currently running). Then, relaunch iTunes while holding down the "Option" key.
You should be presented with a dialog box that reads:
Choose iTunes Library
iTunes needs a library to continue. You may choose an existing iTunes library or create a new one.
Click on the "Choose Library" button, which will allow you to navigate to the iTunes folder on your backup drive. Be sure you choose the actual iTunes folder, and not one of the folders contained within the iTunes folder, such as "iTunes Music."
Assuming your backup was current, you should be back in business, with everything working exactly as it did before your disc crashed.
Once you're satisfied that all is well, create a NEW backup of your entire iTunes folder on a backup drive, just as you did before.
Good luck!
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