I had this issue happen to me where after importing a database of only 10 million nodes, I couldn't create indexes! It would just get hung up and continue to load.
Well, I found a solution, and I hope it helps others!
All I had to do was restart Neo4j after it hung up, and when I went back into the cypher-shell after the restart, the index was created instantly.
I'd love to know WHY this worked! But for now, I'm happy I was able to figure this out, and I hope it helps others. I searched for quite some time for a solution.