What should I do?

When I connected my iPod 4th generation to my laptop it immediatly deleted my purchased music and added new music i've never heard of before. I tried to re-download all my music and deleted the music downloaded by my laptop, but when i re-downloaded some songs were "unable to download at this time". The next day i tried again and the same response happened. What should i do to geet those 8 songs back?