problems with downloading my library to a new computer

I previously had my Ipod synced with my old computer, which was windows XP. I had literally just purchased my ipod like 2 weeks before the announcement was made that Windows was ceasing XP. So, after buying/downloading 12 songs to my ipod, my computer became extinct. I have went till now and finally got a computer that has Windows 7 and I just downloaded Windows 10. I, of course, have downloaded the newest version of iTunes. When I sync my ipod, it registers the Ipod, but, when I go to transfer my purchased songs from it, a message pops up saying I haven't authorized this computer. I immediately go and authorize the computer. Then I try to transfer my purchased songs again, and I get the same message. Also, it will not let me load my music I have purchased in the last 3 days to my ipod. What sould I do?