I have burnt a dvds on macbook pro3,1 running OS10.4.11.[large picture files, jpegs and tiffs which work a treat on lap top] when I put it in mac pro1,1 running OS10.5.8 it shows as a blank disc. Eject and re-enter it a few times and it might recognize it but it might not. check it in lap top and its fine. This happens with a variety of disc types, and sometimes it is fine. Ideas? Steve.