Yeah, like the other guy posted... press x. max lets you turn off the gizmo so that you can see what you are modeling sometimes. However, most people do it by accident and then can't figure it out ...
Ages ago before I knew what X did, I had this same problem and it drove me up the wall. I ended up having to do a complete reinstall to get it back lol.
You can also go to customize > prefrences... > gizmos > transform gizmos. Then check the box next to On. Of course, you can just press X, but just so you know another way if you forget what letter it is or something.
