Did you recently reinstall Windows?  If so, did you install the chipset drivers as the first device drivers installed after reinstalling Windows?  Until the chipset drivers are installed, Windows will not be able to recognize or install any devices integrated on the motherboard, like, for example, the network adapter.

The chipset drivers for your computer can be downloaded from:

http://support.dell.com/support/downloads/type.aspx?c=us&cs=19&l=en&s=dhs&SystemID=INS_PNT_P4_5150&category=0&os=WW1&osl=en&deviceid=1134&devlib=27

The network drivers can be downloaded from:

http://support.dell.com/support/downloads/type.aspx?c=us&cs=19&l=en&s=dhs&SystemID=INS_PNT_P4_5150&category=0&os=WW1&osl=en&deviceid=2966&devlib=5

Steve

No i didnt reinstall my windows, i turn off my computer one day in the morning , and when i want it to use it in the night it didnt apper the network sing, and in the hardaware information it also didnt appear.

Try reinstalling the drivers.

Steve