Where are my albums?

Loaded a load of albums using drag and drop.  These were ripped with Media Player.  At first media player would show them when I clicked on the fuze, when it was connected, but now most of them  seem to have disappeared.  Except they haven’t because I can play them on my fuze.  This is driving me a bit nuts.  Anyone got any ideas?

should have said it’s the same if I use explorer to open the music folder

Sounds like an MTP/MSC issue. Files put on in one mode are not visible in the other. Both will play fine on the player. You just won’t be able to see them on the computer.