My name is Ananya and I work for the Social Media and Community Team at Dell. I regret to hear that your Dell systems is not working fine. Please try the following steps to check if LAN is eabled in BIOS .
STEP 1 - Once you turn on the system at Dell logo Tap F2 key 3-5 times.
STEP 2 - It will show you the phoenix BIOS .
STEP 3 - Using down arrow key highlight "Integrated peripherals" and hit enter
STEP 4 - Check if "On board Lan Controller" is enables if not highlight the option and select Enabled and hit Enter and then Tap F10 once to save changes and restart the system. Please try this step and let me know it if works.
Glad to assist you!
Thanks and regards
Dell Social Media Responder