Old music purchases have gone from my account?

I recently lost my entire music library from my media system (which I use for iTunes as well as other thing), So I reinstalled the enitre system, installed iTunes, authorised my computer, logged in, everything worked perfectly. I then go to download my music purchases. Only recent purchses apear.

I then checked using noth my iPad and my iPhone, the same. Only a few recent purchases apear?

Looking at apps, all of the old purches are there, it just seems to be most of my music collect that I can no longer download.

Having spent rather a lot of money on iTunes amassing a considerable collection I am deeply concerned as to where the huge amount of old purchases have gone?