Q: What happened to my iTunes?

I had thousands of songs stored in the iTunes library, and now when I opened iTunes the window opens saying that it needs a library to use. Well, the last library saved is from 2014 because I upgraded to Windows 10 and my libraries from this year were impacted somehow. Well, I had to downgrade to Windows 8.1 for a website required for a class (they haven't upgraded their site to use Windows 10). Now I'm having to add all that music back into my library, but I can't even do anything at all. I clicked on "create" for a new library which doesn't let me even access iTunes. I'm wondering what is going on? Is it because of the new iTunes? I'm now afraid to upgrade my phone.