Did you reinstall the wireless driver

yes  I already download and run it,  but it still don't work

look in device manager and see if there are any device with a ! or X next to them

Also look at the network listing to see if it is listed

yes it has !next to them

OK first let;s try this.

1. Download the Laptop System Software 

2. Download the Chipset Driver 

3. Download the Ricoh Driver 

place the downloaded file onto the desktop do not run them yet

Boot the computer into Safe Mode. Press the F8 Key at the Big Dell Splash Screen. At the options screen select safe mode. Do not worry if your display looks different as it will.

Once you are at the desktop in safemode  run the laptop software file, then run the chipset file, then run the Ricoh driver file. Do not reboot the computer untill you have all three installed.

Once all three are installed reboot into normal mode.

laptop software can't install in safe mode

Try it in normal mode then. Has there been any change in the devices in device manager.