It was long ago and I forget the details, but there is an older lc pds ethernet card in my stash that will definitely prevent a comparable (LC475) machine from booting. I don't know if the trouble is the card, a missing driver, or the 040 versus 030 implementation of the pds slot (e.g., the 030 implementation allows for a 68882 co-processor, which no workie with an 040). So it's not necessarily logic board capacitors. You might just need a different network card.

What make is it?