i would wash the classic board... wash it with hot soapy water and a tooth brush,  then rinse, and compressor dry off.

the other question is the memory card an apple one or from another company?  

i'v had issues with some memory cards before, causing some of the same kinda thing.  I think Scott Barret had pretty much the same issue,  He had multiple memory cards to try.

but the Mac Classic... and the Mac Classic II and the Color Classic.... these boards almost always NEED to be washed after a re-cap in order to work again.

Its just how it is.