Ipod Help!!

Hello,
Okay so my computer crashed a few months ago and I had all my Ipod music on it. I finally was able to get my computer fixed but they had to wipe my hard drives and then reload all the drivers back onto my computer so I lost EVERYTHING but I still had all my music in my ipod. So I redownloaded itunes and plugged in my ipod so I could transfer my music back onto my computer and get the new updates. The problem is now it will only let me transfer 65 of my 700 songs I have on my ipod and to get the new update it says it has to delete all the music I already have on my ipod... I want to have my ipod updated but if I lose 600 songs theres no way to get it all back without rebuying everything! Is there a way to tranfer the rest of the music onto my computer???