I would suspect that there is a problem with your start-up scripts . . . . which means either re-install Maya or . . . make an attempt to find the script that controls the cursor and just replace that script.

You *might* be able to find the script that controls it, (if the coding for it is not C++), by searching the Maya scripts folder for something that would be associated with the cursor. For example, we know that the cursor runs in the graph editor, so if you could find the script for the graph editor, you may be able to track down where the cursor is scripted. How? I'd do it by doing a search for a string that is most likely unique for the graph editor, like "break tangents" and see which files contain that string. Then I would look for something that calls a function for the cursor. If you can find that function, you can probably figure out exactly which MEL script controls the cursor and find someone to send you that script who has the same version of Maya that you are running.

You could also try Maya tech support . . . .

Either way, there is probably no real EASY fix . . . . but hopefully this is some food for thought.