WHEN I TURN IT ON ALL THE GREEN LIGHTS LIGHT UP

I guess this is not an intermittent issue though right? Kindly do these process/procedure if things able to work.
1. Remove the Optical Drive.
2. Remove the Hard Drive.
3. Remove all memories (RAM).
After removing those devices try to turn on the laptop eventhough it produces beeping noises and stay in the BIOS screen. Have to observe if it restarts again or shuts down on its own. If the scenario appears that it is still shuts down after 5 seconds then, motherboard is not working properly. Actually there would be more troubleshooting steps for this to isolate the issue. If you can able to follow some of the steps then my piece of advice is to call Dell technical support for some assistance by removing some of FRU devices. Things are more likely critical. If you're unable to do the thing then have then replace the laptop in this regard if it is still under warranty. That's one of a good thing. Hope things will help you to determine. Thank you.