It's a bad mainboard -- if under warranty, call Dell for repair. If you need a part reference, post the complete model number (7765, etc.) and the CPU you have and someone can find the correct replacement board.
Thank you for your message. I will be glad to look into this for you.
The display is working fine & this seems to be an issue with the motherboard.
If you are comfortable, remove the memory & start the computer check if there are beeps heard.
For my reference, please click on the message tab next to your avatar– click “New Message” & search for my Dell username (Dell-Sreejith R) & send a private message with the service tag, registered name & email address.