Q: In store preferences automatic downloads I find the the box Apps and Books. But im missing the button Music. Whats wrong??

What country are you in ? Music can't be re-downloaded (automatic downloads is effectively a type of re-downloading) in all countries. If you aren't in a country where music can be re-downloaded then you will need to copy it from the device or computer that you buy it on over to that computer, instead of it being automatically downloaded from the store on it.

What can be re-downloaded where : http://support.apple.com/kb/HT5085

Looking at that link, music can't currently be re-downloaded in Norway, so you will need to copy your music purchases between your computers/devices yourself, you won't be able to download it on each.