Transferring iTunes library after Windows upgrade broke link to some songs
How many songs? If it's just a few, then the easiest way is to do it manually. Just try to play the songs in question, and you'll get a popup saying the file couldn't be found, and offering to choose a new location. Do that, and select the file in its new folder. That will restore the file without breaking your playlists or metadata.

If you have more files than is practical to manually resort each one, you can edit the iTunes Library.xml file to do a find &amp; replace, then scrap your .itl file and import the XML file, which will restore your playlists and files.

For more information on this process, read Apple's support site and this guide.