upgrading to iTunes 7.6 lost all my music

Dec 18, 2007
i have a terrible problem! i am sure most people might have experienced this. i had my ibook G4 upgraded to tiger and iTunes 7.6 and i can not locate my music. my playlist is there but when i want to play any of the songs it puts a ! like sign in front of the song and asks me to locate it but they are no where in my computer.i tried to downgrade to 7.3 and 7.4 this time it says 'iTunes library cannot be opened because it was created by a newer version of iTunes'

could someone please help me and sho me a way or a solution. i am totally lost!
thank you.