Solved it for myself. I forgot I had been running Synergy, it's a kb/m sharing software for multiple desktops. For whatever reason it doesn't play nice with NS2. Turned it off and everything is peachy.
I have recently gotten this issue. I have tried reinstalling the game, clearing my settings, nothing seems to fix it. The game will play fine and then at seemingly random times the keyboard and/or the mouse input won't work, or will be slow/unrespos…