kadri,   Make sure that the wireless adapter is enabled in the BIOS, press F2 at the Dell Screen. Save changes and exit.   You tried to install the drivers, so anything in the device manager that has a yellow exclaimination mark or red x, right click, uninstall.   Restart your computer. The new hardware wizard will install the device/drivers when the computer restarts and the unrestricted account logs in.   Other option is that the wireless card came loose or has failed. Instruction HERE <ADMIN NOTE: Broken link has been removed from this post by Dell> to remove and reinstall the wireless card.     Rick    
Hey! I have Dell Inspiron 640m and I seem to have a problem with my wireless connection.The WiFi light on my computer went off all of a sudden when I was browsing the Internet and now I can't connect to wireless anymore. Wired connection works just fine but my computer can't find any wireless networks at all though there are plenty around. Fn+F2 only turns Bluetooth on and off, the wifi light stays off all the time. I have never had any problems with my wireless connection before and I haven't changed any settings, although my Vista did update itself the day before (maybe that caused some problems?). When trying to open my Wireless WLAN Card Utility, it first says that 'The wireless network adapter could not be accessed. This application may have diminished the functionality as a result.' The Site Monitor tab says that radio is disabled and when I run the tests in the Diagnostics tab the results of all the tests are 'failed'. I'd be very thankful if anyone knew if there's any way to fix this problem at all. Thanks!
Dell Inspiron 640m - wireless suddenly doesn't work