Recently upgraded to Win 10 (well, why not?)
I've noticed this happening in game occasionally...
I can get it back to normal by going into options and changing screen mode, but curious if anyone else has seen this?
Using a GTX960 with up to date drivers.
I have had this on my old Win 7 machine before in a slightly different way (as in: the pointer stayed in the weird blue arrow mode all the time - annoying). It was related to Alt + Tab - ing between different tasks on a 4-year old system that had accumulated some clutter over time and had slowed down in the process. The only way to solve it was to restart the game and not switch tasks until all the background stuff had run its course (including virus profile or steam updates). Not switching tasks once ME3 starts never produced this.
I suspect this was due to some weird bug switching between screen modes during Alt+Tab. Maybe it is the same in your case. Good Luck
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EDIT: I did not try the changing of screen mode you mention. I have not encountered it yet either on the new Win 7 one or the Win 10 Notebook I use to play.