I am not able to connect to internet by wireless but I can connect through ethernet cable, i am having a dell inspiron 1525 laptop with Vista OS
I had a similar problem with a brand new Inspiron 1525; it just refused to recognize any wireless networks.
The solution was to remove (Uninstall) the Dell WLAN Management software this removes the device as well. Then Reinstall the wireless card with the Drivers ONLY. (It seems the DELL software doesn't work properly with the DELL branded network card in a DELL Laptop; go figure)
When you download the driver it will unzip and try to install automatically; but this will only reinstall the offending software again, so you must cancel the installation after you unzip the file.
When I searched for new hardware again it found the device as a Broadcom wireless card but could not install the drivers. This allows you to click Update Drivers and point to the 'drivers' folder in the location that the files were unzipped to. Once the device driver alone is installed the wireless card works immediately and finds any available networks.