hi there ,
I'm assuming windows 10 is on the system....
I'd suggest you check WIFI switch is turn on in Settings. If switch is turn on then I suggest you turn off for a few seconds and then turn switch back on. At left bottom of taskbar, please click windows icon, click Settings, Network & Internet, and then WIFI.
What is the current OS installed on the system?
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://bit.ly/1JEw2ov
Does the ethernet work fine? Check if the wireless card is detected in device manager under network adapters or check for any unknown devices in device manager.
As advised by LSUFAN51, check if the BT is turned on.
If yes, then use the fn + prtscr key on the keyboard to enable / disable all wireless devices when prompted again during installation.
Create a local admin account and reinstall the driver if required and check if the wireless works - http://bit.ly/1JoFhcw
Also, please click my DELL-username and write me a private conversation with the service tag and your contact details(Name and Email) for case records.
Let us know if you have any other queries.