PLEASE HELP! Itunes library gone but music still on iPod

I recently have started organising my 'my music' files and deleting folders with more than 3 copies of songs, I have a lot of music 2500 songs and opened up itunes and all music I have imported (not bought) has gone, my music is still on my ipod though but I'm too scared to sync it in case all my music has gone, I still have my original music in 'my music' file but it's not shown up on library as usual PLEASE HELP!