Exclamation marks next to my songs in itune?

Today I was looking for a song on my iphone and noticed that it had disappeared, so I plugged my iphone into my computer and saw that all of my songs had exclamation mark next to them. I googled my problem but no help. I know that this problem happens because itune can't find the location of my songs, but I've been manually put in my songs for the last 3 years and there's no way that I can restore all of them. Please help. I don't put all my music in one folder.

If you run itunes then right click a missing song and select "Get info".
When the message to "locate" the missing file select "NO".
The info windows will now open, click the "summary" tab (At the top)
Itunes expected location/address is "Where" ( Shown at the bottom)

If you manually go to the location of any song file shown as missing in itunes, is it there?
(Has the address changed at all?)

Do you keep the itunes media folder in default location (music)?
Is the music (Shown as missing) stored in any location other than "C" drive ie "D" or external drive?
Can i assume that in itunes advanced settings that songs files added to library are not copied to itunes media folder.ie ( music Files in other locations must remain)?

Will look back later…