turn off machine unplug everything but the power plug from cpu, see if it then boots. if yes then something is plugged in wrong. If not put the old ram chip back in and see if it will boot. If it works ram may be bad or or bent pins.

Also, take your index finger and press the chips in, including the large ASIC in the center. The DCS board can boot completely independent of the main CPU (as you're hearing).

I've seen this when the ASIC rattles out of place or the pins get oxidized.

yes the 3 ribbon cables and the switch inputs at the bottom of the board. leave the plug under the short ribbon cable. there will only be the one plug.
If it works the top led will come on and go out, the middle one should start flashing. If this happens then the board is working.

In case this helps. On my NBA Fastbreak that was working fine I installed a new ROM and then it wouldn’t boot even with everything disconnected. Pressed on everything, reinstalled original ROM, nothing. I ordered a chip extractor and pulled the ASIC and reseated. Booted up after that. Had some weirdness and popped out CPU at U4 and reseated and things are ok now. Been a couple weeks. Wouldn’t think just changing ROM would do that but it did. Maybe installing the NVRAM was enough to wiggle things a bit.?????