Thank you again for your good advice.
The song files themselves are not corrupted. They can be played with alternative players.
I've deleted the former and reinstalled the latest version of ITunes. The new version made no attempt to import my old library. It would appear I'm essentially starting from scratch.
Now, how do I get my music back into Itunes? I can import files from my Music Library file into Itunes, one at a time. Is there a more time-efficient way to do this? Itunes will not allow me to import the entire folder at one time-it requires that I go into the actual song files and select them for import. Is it possible to rename that folder so that Itunes imports it automatically upon start-up? Is it possible to reverse synch my Ipod to upload from the Ipod to Itunes?