I was transferring music from my (windows) laptop to my iPod 4. Some transferred, then all of the music(except for what I had bought from iTunes)was gone. Then, it started saying "updating files at the top of the computer, but nothing happened. HELP!

Ok, so I transferred some songs using my USB cable. Then, I checked my iPod, and it had spaces where there would be songs (ones that I had transferred from my laptop when I first got my iPod, so not bought from iTunes) but they were blank, so I completely turned off my iPod and turned it back on, that's when all of those songs disappeared, but they were still on my computer. Only the ones I had purchased iTunes on my iPod remained. I got some other songs to transfer after that, then it started saying "preparing to update files on iPod" "finishing updates" then it doesn't say anything and the songs still aren't on my iPod. Please explain and tell me if there is a way to fix it!😠😟😕😢