There was a topic a wile ago about the mouse bug where it suddenly stops working and you have to keep pressing Esc until it works.
For me when i started the game up it wasent working at all and i could not get it to work.
I found out that on the game startup if you skip the loading screens using the mouse button the mouse works fine without any problems.
I dont know if it will work for anyone else or help at all but i thought i would share anyway.