Without any warning, my E7440 no longer powers on. I tried the hard reset with 30 or 60 seconds pressing power button after removing battery and unplugging power method, doesn't work. There seems no POST either according to DELL website. After pressing power button to start, the power LED will stay on for for at least 15 seconds, then went off and battery LED is on for less than 2 seconds. After that no LED.

I have reseated RAM already, not working. Is the mother board is bad? What is the indication of power LED and battery LED. I don't see any amber lights, nor blinking according to this page: https://www.dell.com/support/article/us/en/04/sln309632/a-reference-guide-to-the-latitude-notebook-and-tablet-diagnostic-indicators?lang=en. Any hints? Is power supply or mother board? failure?