I ve gx270 dell,because of some reasons I ve to format the system, and now there is no sound driver.I ve installed right sound driveR required, I ve updated bios and installed chipset driver . But still doesn't seems to be working, hepl

Head over to the Dell site as they have all the drivers.
Just put in your tag number and it will give you what you need.

Try this link: Drivers & Downloads (http://support.dell.com/support/downloads/driverslist.aspx?c=us&l=en&s=gen&os=WW1&osl=en&catid=&impid&SystemID=PLX_PNT_CEL_GX270)