Why do I have to repeatedly sign into iTunes to no avail to access the very songs I've paid for?

I am so disgusted that I have to repeatedly try to sign in to my iTunes account and continue to have to sign in again and again! My password is correct every time and I have the latest version of iTunes installed and I have Windows 10. If I try to click on 'Cancel', a box then appears with the word 'password' and that word jumps constantly preventing me then from closing the window or minimizing or switching to my desktop so that I have to actually re-start my computer just to get rid of it!! I cannot understand why it's so difficult to get any help from APPLE?? I hope that someone that has had the same problem will be kind enough to help me out here with a solution.