When you can’t drag and drop in iTunes, look at the column headings to see which one you have selected — it will be highlighted. Then select the farthest left column, which has numbers in it — THAT’S the one that allows you to drag and drop songs to play in the order you prefer. What is the logic of this? ONLY the numbered column lets you change the order in which songs will play to your personal preference because dragging and dropping a song when the number column is selected allows you to change the number of the song. All of the other columns will play your list in the sort order that goes with the title of the column: name, artist, composer, album, genre and so on.
Also, make sure you don’t have a playlist set to “Shuffle” or “Random.”
Ah, computers! Making tasks that should take all of five seconds suck down well over an hour.