Currently Being ModeratedJun 9, 2013 3:46 PM (in response to TT24601)
First, find the songs on your computer. They should be located in Music/iTunes Media/Music if you kept the option enabled to automatically keep the iTunes Media folder oraganized. Otherwise, the files could be spread out anywhere in the filesystem.
Once you find them, you need to restore them back to the location iTunes expcets them to be, which you can determine by secondary clicking a song, clicking Get Info, Summary tab, and note the Where location at the bottom.
If that is too much work, and you kept your library organized, you could restore from a Time Machine backup to get back to exactly how it was at an earlier point in time. Just restore the entire iTunes folder under Music.
Currently Being ModeratedJun 9, 2013 5:58 PM (in response to TT24601)
Where were the actual music/video files at? Are they still there? If so you will just need to use the "Locate" button in the error window that pops up to point iTunes to the correct location where they are actually at. If they are not there and you use Time Machien then you can can pull them from the most recient backup that they are still present in. If you do not have a back up of them you can re-download the ones you purchased from the iTunes store via iCloud.