Problem with Random Firing

[Duff Matthews]

Right ok i get a problem of random firing when playing the game also it randomly cycles through the wepons everything else is fine with the game but i cant play it because he just fires his gun wenever he wants. i'v seached the internet to see if anyone else has this same problem but i cant find anyone who does.
im running vista 64 and a dual-core processer witch runs crysis fine on high settings.

Anyone one experencing the same problem or know if theres a fix?
Cheers