Counter Strike 1.6 Problem in Windows 7

Hi, When i connect to any server in the game. every thing works fine. but when i press W (key to move forward) and D (key to move right) it moves fine. but when i leave the D key. it stops walking. even i have pressed W key. Please help me in this. It is not only in this it also happens when i change my gun. And there is no problem in my Keyboard. i also asked my friends about this problem they suggested me to reinstall the game, and i have did it.