iPod touch error in playlists

How do I fix songs that have the msg "The song __ could not be used because the original file could not be found. Would you like to locate it?". I am not good with computers and have over 60 songs being held hostage. I started iTunes on a work computer but it crashed, then put on another computer that eventually crashed. No way to go back to those computers to try to fix anything. I'm on my 3rd computer and this is driving me crazy. Way too many songs that I've purchased to just let go. Any help would be appreciated.