I would suggest you to update the BIOS and then uninstall and reinstall the Wireless card driver on the system. Please enter your service tag # on the link below, select the OS and then download the BIOS from BIOS section and then wireless card driver from Network section onto the Desktop screen.

http://dell.to/18r60nI

Please follow the steps mentioned below to uninstall the wireless card.

1. Open the charms bar by moving the mouse to right top corner of the screen and inthe search box, Start typing devmgmt.msc and then press enter.

2.  Select the wireless card and Bluetooth device under Network Adapter and right click on it

3.  Now select properties.

4.  In the properties window, under Driver tab, click on Uninstall button.

5.  Check “Delete the driver software for this device.”

6.   You want to delete the driver click OK.

After the uninstall finishes restart the system and install the drivers by using the file downloaded on the desktop screen.