ipod classic doesn't sync all movies and music

HI all, I have an ipod classic and have a pc-based laptop running Windows 7 Home premium. My itunes library is housed here. I have the media folder located on an external hard drive connected to this laptop. I haven't used my ipod much in the past past but lately have been using it more and have noticed that songs are "missing". I do also have a new pc laptop running windows 8.1. I have loaded songs fron old cd's etc. using this new laptop.

When I went back to the "old" laptop to sync the library with my ipod, I can see at the bottom that I have many more movies and music indicated by the color bars and see that I hit "sync" and the bars change to the "old" music and movies library and see that it says it's syncing (and I've set the library to sync ALL movies and music and I have PLENTY of room on both the ipod and the External HD). But then after a few moments, the colors revert back to my ipod and there really isn't any sync that happened.

How can I get my itunes Library to sync with my ipod and not lose the new songs that I added from the new laptop. Am I missing something here? I feel like this shouldn't be so difficult to do, yet it is!

Thanks in advance for any help. The ipod I am using is a 160GB.