Thanks for replying
Well the last result is :
I have case front fan for hard drives, back fan. cpu fan , power fan and vga fan.
intrestingly the power is not making "annoying-noise" .It is the graphic card. I'm still surprised about it, I pulled it out and turned the pc on, and become sure that it is causing the main sound.
I go check what is wrong with "BFG, geforce 7600 GT OC".
edit :
http://shopping.yahoo.com/p:BFG%...e=user-reviews
look at review cons.
:/ now i'm really confused, don't know what to do !