It's a common problem with Itunes but simple to be fixed.

On a Mac, just go to your user account, then to you Music folder, then to your Itunes folder,delete off the Itunes Library file and iTunes Music Library.xml file. Then your should be able to use iTunes normaly again.

What you are deleting is the iTunes database of your list of songs in your iTunes folder, and not your MP3 files itself. After deleting it, you'll just have to drag your songs into iTunes again.

If you don't want the hassle of relisting your songs again, try this first. Copy the Itunes Library file and iTunes Music Library.xml file to another temporary folder, and the delete the original file. Launch iTunes. iTunes will automaticaly create a library and .xml database file. Close iTunes again and replace the newly created file with your copied one. You should have all your songs listed in iTunes again.

Hope this helps.

Yes, under My Document, go to My Music folder and then Itunes folder. You will see three files, the Itunes .xml file, Itunes Database file and Itunes folder where all your ripped MP3s are stored by default. Just delete the .xml file and database file and you'll be up and running your Itunes.