My Ipod doesnt show the files on my Itunes - Please help

I dont have access to the original computer i used to install itunes and load songs onto my ipod nano when i first bought it. Now when i connect my ipod to a differnt computer Itunes doesnt see the files that are already there, is this normal and if so have i no way to remove the old files??? Also, my Ipod dosent show any new files I create on Itunes even though it tells me the update is complete,Everything else seems to be fine, i have changed the letter of the drive where the ipod is located as suggested to another user, i have also tried four of the five R's but this has had no affect. I am reluctant to try the fifth R incase I end up with no music atall - would greatly appreciate any help!!!