Music won't sync to iphone 4s?

So I'm trying to sync some music to my iPhone but it isn't working. At first the problem was there wasn't enough space. I fixed that issue but now iTunes is being stubborn. I selected the option for my entire library to sync to my phone but the music is there on my phone, but its greyed out. And on my iTunes there's a dotted circle next to the songs I'm trying to add. I don't know what to do!

First take off the ✔ to fill empty space with music. You could be there for. Long time every time. Try playlists. You have multiple copies of the same music on iPod. That's is why they Are grey and won't play. You need to restore your iPod and start over. It happened to me. Frustrating