Music disappeard on iPhone after iCloud



My former MacBook with Panther died after 6 years of extreme use :/. I bought a new one with Lion.
I was using Time Machine regularly so I've got no problems with getting back my stuff EXCEPT for iTunes library.
I've got my iPhone synced with the other computer, so when I activated iCloud all my music disappeared from the iPhone.
When I connect it to the computer I can see that there is about 5,8 Gb of audio files on the phone but I can't access them.
What can I do to have my music back and save them on iCloud to have them also in my computer?

Thank you for any tips!