Try Cleaning the contacts on the chip and fast ram sockets and reinstall or replace the ram with good known simms.
this could also be a case of caps leaked on the A3640 accelerator and have eaten a trace that runs under one of the caps, i have seen this happen to loads of boards in the last 20 years. If you remove the caps check the traces for continuity carefully. Its been my experience the 4000 will boot with a 3640 with no caps for quick and dirty testing on 3640 trace repair.
Another possible problem is the fast slot on the accelerator,the pins may be dirty or not making full contact.
