My name is Vishal and I work for the Social Media and Community Team at Dell.
Please find the below link for your Optiplex 380 Internet Drivers:-
1) Lan Drivers:- http://dell.to/M0OfSU
2) Wireless Drives:- http://dell.to/LebdUb
Please install the above drivers for your computer, and I am sure you will be able to connect to internet.
Please let me know if you need any more support from our side.