Hello and thank you for visiting Fixya Support, I will be glad to assist you.
There may be an issue with the iTunes application, the hard drive or even connection problems
I have an article which is can aid you in resolving the issue of your songs not uploading.
Link: Why Can't I Put Songs on My iPod?
It is an easy to follow guide, but also detailed ebough to help resolve the issue with
your songs not loading into your iPod.
I also am providing this short tutorial on just how to upload songs using iTunes
Link: Uploading Songs to your iPod using iTunes
I am sure you more than likely know how to upload songs, but just in case, I am providing this good article for your benefit anyway...
I hope this helps, however if you have more questions, please feel free to reply back to this post.