No POST. Device turns on, but no display and wont boot. Help pls

Lenovo T570 laptop turns on after replacing the SSD adapter board inside (original one had cable connector come off). Turns on immedately when plugged in. When on battery it waits for me to press the power button to turn on. Power button led turns on solid green. Keyboard backlight and num lock / caps lock LEDs briefy (about 1-3 seconds) light, but then turn off. Power button led stays on solid green. No display or visible response to tapping caps lock or num lock keys. Fans remain running. Occasionally (rarely but did happen a couple times) does boot into BIOS but doesn't recognize the ssd.

Troubleshooting completed:

-Power cycle (unplugged both batteries, held power button for 30 secs)

-BIOS reset using cmos battery

-CMOS battery replacement

-Checked RAM, tested each separately and in opposite slots

-Tried with one battery disconnected (this model has an internal and external. tried both ways)

-Unplugged the new ssd board, no change.

-Tried the reset button at the back

I'm out of ideas at this point. Any idea what this could be? Thanks so much!

ETA: Now after holding the reset button w/ batteries unplugged it's doing a beep chime. Attached