Mac killing off my songs.. one by one, showing the (!) exclamation point

Question

I got my macbook pro in July, and everything has worked fine. The only problems I've had are with my itunes. I transfered all my music from my old computer onto my new itunes and onto my new ipod, and it all went fine. Then a week or two later I tried to listen to a certain artist, and half the songs were missing. As I clicked to play them, the exclamation point would pop up. So I followed the window and went looking through my files to revive them, but they were nowhere to be found. I searched my whole hard drive for them, and they were no where. I then realized that this was happening with other artists too. A song here or there, and then whole albums would have that . My computer simply erased them. They were even still on my ipod. Luckily I still have all the files on my old desktop so I recopied them, and figured it would be fine.
Not really.
After I fixed those songs, my computer just erased a few MORE. Just random songs. They'd just be gone from my computer. Poofed out of thin air! I moved away and can't go retrieve them from my old computer, and I refuse to have to always do that. My computer should not be doing this. Slowly, one by one, another song will go missing, one by one. Now, it has started happening to my purchased items! Ones that I just bought a few weeks ago! Disappeared! Sitting there with that stupid in the "purchased" playlist!
I'm really sick of it and would like some answers. How can I retrieve these? I heard there's a form on the site to state a claim so they will allow you to redownload your purchased items, or send them to you or something, but I couldn't find it. And I'd really just like itunes to stop killing my files.
Please help!!

Answer 1

try if this script helps:
_*iTunes Track CPR v1.3*_
This script attempts to locate the files of so-called "dead tracks"--iTunes tracks designated with (!)--that you assume are not actually missing but are still located in the iTunes Music folder in their "iTunes File Order" (Music -> Artist -> Album -> file.xxx)."
also useful:
_*Music Folder Files Not Added v2.0*_
This application will list the file paths of the files in your designated "iTunes Media" folder which are not in iTunes' library. Additionally, you can select a different parent folder and its contents will be compared to the iTunes library. Options to Add a selection of found files to iTunes or move them to the Trash.
JGG