What is the current OS installed on the system? Does the ethernet work fine? Is the wireless card detected under network adapters in device manager? Did the issue start after any recent windows updates?
If the system was working fine earlier, then perform a system restore to restore the machine to an earlier point where it was working fine - http://dell.to/1Sg6khF
Update the BIOS if possible - http://dell.to/2fIMORn - restart the system and check if it works.
Restart the system and press f2 on startup to enter BIOS - check if Wireless swtich and wireless devices are enabled in BIOS.
Restart and check in safe mode with networking.
Enable the built in admin account and check - http://bit.ly/1Bgok2R
Also, please click my DELL-username and write me a private conversation with the service tag and your Name for case records.
Let us know if you have any other queries.