Problems with itunes on my windows computer

hi, i'm currently having a problem with itunes on my windows computer.

so i like using an ipod and download lots of songs on it but recently my computer has been telling me to enter my apple id password and when i enter it correctly it still asks for it. also, it is telling me that it can't download songs onto my ipod because i don't have an apple music subscription. my sister is an expert on ipod's (since she did a lot of research on how to fix one) and i asked her and she said that shouldn't be a problem because if you buy the song it shouldn't have anything to do with an apple music subscription. its also not syncing the songs that i buy from itunes and its never done these things before. i'm pretty sure its not the ipod though.