iTunes won't let me sync my music from my desktop to my old 5s while it works fine on my laptop.

The reasons for this post are quite simple. My laptop is dying and I want my music to listen to (which I think is a perfectly relate-able reason). The 5s in question is actually my mom's old phone. I broke my last one, she got a new 6 and I transferred my data and number to the old 5s. When I go to iTunes on my new desktop (home built 😉), the sync button is always grayed out and disabled. Also, iTunes does not let me manually add music to my phones playlist. The only way I can add music is with the Autofill feature, at this point the songs are on the playlist, but are "ghost" songs (grayed out and they have the dotted circle next to the name). Finally, the usage bar at the bottom of the window shows all orange ("Other" category) and free space (7.64 GB).

For the record, the songs I am trying to sync are not bought from the iTunes store, they are songs accumulated over the years, and currently the phone has no music on it.

I have tried the following methods:

1) Reinstalling iTunes

2) Making a completely new iTunes library

3) Restarting my PC

4) Checked all the settings I could possibly think would affect this

5) Made sure my computer is authorized

6) Deauthorized and reauthorized my PC

7) Made sure I was using the correct apple ID

8) Backing up and completely restoring my Iphone to original settings and data, then restoring from the back up

9) Used a different USB port (both from the front of the PC and directly from the motherboard)

10) Bent backwards in desperation and frustration