Has this always happened since you replaced your keyboard, or is this the first time you've tried BF2 since? On my old keyboard, I wasn't able to scope, lean, hold breath and move in CoD2 at the same time (a+q+shift) because of some key input blocking thing. Replacing my keyboard remedied that. Maybe you've got the same problem, but in reverse? Also, make sure your keyboard drivers are installed. If those don't work then BF2 is probably messing things up, like shift allocated to more than one command etc.
Also, when you press all those keys together (w, sprint and such) does you computer make an internal beep?