Alienware 17 R4 not powering on, power button and keyboard flash only

i just picked up this alienware 17 R4 which isn’t powering on. i have the correct charger.

the power button illuminates blue along with the alienware marque and the keyboard, then the machine cuts off shortly after.

if i pull the RAM, i get the correct diagnostic LEDs for no RAM, and the machine stays on. if i pull the CMOS battery, i’ll get the correct diagnostic LEDs for bad CMOS battery after a few power on attempts, but it still cuts off. i have replaced the CMOS with two different known good batteries.

i have disconnected all power sources and held the PWR button for 30+ seconds with no results. i have attempted to power on with batt only, AC only, and both.

i have also tried known good ram from another dell i have, as well as tested both 8gb sticks in the other dell. all ram is good.

any ideas?