when i am playing normally i have 100 fps but when someone write something my fps go down to 50 u know some command or other things to that not happens?

"when someone write" Do you mean in-game, friends or on Msn/Icq?

If you know that your computer is good (for cs atleast) it might be something bugged (it can't be some command wrong atleast).
So, have you tried to reinstall cs?

ingame

i never had that problem , but now :\