Dell Precision 7670 suddenly shut down and now completely dead — charger LED also went out

My Dell Precision 7670 suddenly powered off while I was using it. The laptop was not under heavy load and was not noticeably hot.
At the exact moment it shut down, the LED on the Dell AC adapter also went out. After unplugging the charger and plugging it back in, the charger LED came back on.
Now, when I connect the charger to the laptop, the charger LED stays on continuously, but the Precision 7670 shows absolutely no signs of power — no power LED, keyboard lights, fans, diagnostic light, or response from the power button.
I’ve already tried disconnecting the charger and holding the power button for around 30–40 seconds, but it didn’t help. I currently can’t open the laptop to disconnect the internal battery.
Has anyone experienced something similar with a Dell Precision 7670? Could this be a motherboard/power-management issue, battery protection state, or DC-in circuit problem? Any troubleshooting suggestions before I take it to Dell service?

Thanks