There are two quick ways to fix this annoying problem.
1. Go to the very bottom of your screen (right underneath the bottom scroll bar), where you will see the letters REC, TRK, EXT, and OVR. Double-click on "OVR" and the problem will go away.
2. Press the "insert" button on your keyboard. It is located above the arrow keys, next to the "home" and "delete" button.
This happens to me all the time and I've been tought how to fix it in computer class.