Good morning, Before I investigate further, has anyone else using a PC found that the mouse becomes inoperative as soon as the game loads? I can move the cursor around but have to use the enter key to select all options in the menus and the mouse becomes useless once the service is loaded. The only cure is to validate files in Steam then it runs fine until the next time when my mouse doesn't work again. I've updated my mouse driver, unplugged it and plugged it in again. The mouse works will all other PC tasks so isn't faulty.
Happens to me as well. If you switch to another window, for example clicking on a second monitor or using alt-tab, and then go back to the game, it should start working again.