Ok so this is a weird one. In gog Galaxy the mouse pointer occasionally switches to the windows pointer in a section of the screen and doesn't work in game. For example, the pointer in dungeon keeper 2 is an animated hand. Works just fine but there will be a section of the screen were the windows pointer pops up and you can't click on anything in game. Alt-tabbing out of the game will fix it, but some games crash when I alt-tab. (Sunless sea for example. Thanks for that one btw :) it's great)

Good luck lol

Try switching to another USB port or make sure its cable inside the computer is alright. If that did not help, try with another mouse. Still not working? Check that your RAM and hard disk are alright as slight problems there will damage files, drivers included, and cause odd problems.

Got something running in the background beside the game and Galaxy? Sounds like you;re losing focus and windows is trying to point you to another program.